Allegheny was the first county in Pennsylvania to be given aNative American name. It was named after theLenape word for theAllegheny River. The meaning of "Allegheny" is uncertain. It is usually said to mean "fine river". Some historians state that the name may come from a Lenape account of an ancient mythical tribe called "Allegewi" who lived along the river before being taken over by the Lenape.[3]
Prior to European contact, this area was settled for thousands of years by succeeding cultures of indigenous peoples. Duringthe colonial era, historic native groups known by the colonists to settle in the area included members of western nations of theIroquois, such as the Seneca; theLenape, who had been pushed from the East by European-American settlers; theShawnee, who also had territory in Ohio; and theMingo, a group made up of a variety of peoples from more eastern tribes.
European fur traders such asPeter Chartier established trading posts in the region in the early eighteenth century.
In 1749, CaptainPierre Joseph Céloron de Blainville claimed theOhio Valley and all of western Pennsylvania for KingLouis XV of France. The captain traveled along theOhio and Allegheny rivers. He installed lead plates in the ground to mark the land for France.
Most of the towns during that era were developed alongwaterways, which were the primary transportation routes, as well as providing water for domestic uses. Through the eighteenth century, both the French and the British competed for control over the local rivers in this frontier territory of North America. Native American bands and tribes allied with the colonists to differing degrees, often based on their trading relationships. The British sent MajorGeorge Washington to expel the French from their posts, with no success. He also nearly drowned in the ice-filled Allegheny River while returning to camp.
The English tried again in 1754 to establish a post in the area. They sent 41 Virginians to buildFort Prince George. The French learned of the plan and sent an army to capture the fort. They resumed building it and added increased defensive fortification, renaming it asFort Duquesne.
Given its strategic location at the Ohio, Fort Duquesne became an important focal point of theFrench and Indian War. The first British attempt to retake the fort, theBraddock Expedition, failed miserably.[4] In 1758 British forces under GeneralJohn Forbes recaptured the fort; he had it destroyed to prevent any use by the French. The British built a new, larger fort on the site, including a moat, and named itFort Pitt. The historic site has been preserved as Pittsburgh'sPoint State Park.
Under their colonial charters, both Pennsylvania andVirginia claimed the region that is now Allegheny County. Pennsylvania administered most of the region as part of itsWestmoreland County. Virginia considered everything south of theOhio River and east of theAllegheny River to be part of itsYohogania County, and governed it fromFort Dunmore. In addition, parts of the county were located in the proposed British colony ofVandalia and the proposed U.S. state ofWestsylvania. The overlapping boundaries, multiple governments, and confused deed claims soon proved unworkable. Near the end of the American Revolutionary War, in 1780 Pennsylvania and Virginia agreed to extend theMason–Dixon line westward. This region was assigned to Pennsylvania. From 1781 until 1788, much of what Virginia had claimed as part of Yohogania County was administered as a part of the newly createdWashington County, Pennsylvania.
Allegheny County was officially created on September 24, 1788, from parts ofWashington andWestmoreland counties. It was formed to respond to pressure from the increase in settlers living in the area around Pittsburgh; this was designated as thecounty seat in 1791. The county originally extended north to the shores ofLake Erie; it was reduced to its current borders by 1800.[5] As population increased in the territory, other counties were organized.
In the 1790s, theUnited States federal government imposed awhiskey excise tax. Farmers who had depended on whiskey income refused to pay and started the so-calledWhiskey Rebellion after driving off tax collectorJohn Neville. After a series of demonstrations by farmers, PresidentGeorge Washington sent troops to suppress the frontier rebellion.
The area developed rapidly through the 1800s with industrialization. It became the nation's primesteel producer by the late 19th century and Pittsburgh was nicknamed "Steel Capital of the World".
In 1913, the county's 125th anniversary was celebrated with a week-long series of events. The final day, September 27, was marked by a steamboat parade of 30paddle wheelers. They traveled fromMonongahela Wharf down the Ohio to theDavis Island Dam. The boats in line were theSteel City (formerly the Pittsburgh and Cincinnati packetVirginia), the flag ship;City of Parkersburg,Charles Brown,Alice Brown,Exporter,Sam Brown,Boaz,Raymond Horner,Swan,Sunshine,I. C. Woodward,Cruiser,Volunteer,A. R. Budd,J. C. Risher,Clyde,Rival,Voyager,Jim Brown,Rover,Charlie Clarke,Robt. J. Jenkins,Slipper,Bertha,MidlandSam Barnum,Cadet,Twilight, andTroubadour.[6]
According to theU.S. Census Bureau, the county has a total area of 745 square miles (1,930 km2), of which 730 square miles (1,900 km2) is land and 14 square miles (36 km2) (1.9%) is water.[7]
Until January 1, 2000, Allegheny County's government was defined under Pennsylvania's Second Class County Code. The county government was charged with all local activities, including elections, prisons, airports, public health, and city planning. All public offices were headed by elected citizens. There were three elected county commissioners.
On January 1, 2000, the Home-Rule Charter went into effect. It replaced the three elected commissioners with an elected chief officer (the County Executive), a county council with 15 members (13 elected by district, two elected county-wide), and an appointed county manager. The changes were intended to maintain a separation of powers between the executive and legislative branches while providing greater citizen control.
The county has 130 self-governing municipalities, the most in the state.[13] (Luzerne is second with 76).[14] The county has one Second Class City (Pittsburgh) and three Third Class Cities (Clairton,Duquesne, andMcKeesport).
A 2004 study found the county would be better served by consolidating the southeastern portion of the county (which includes many small communities with modest economies) into a large municipality ("Rivers City") with a combined population of approximately 250,000.[15]
Allegheny County has a Home Rule Charter form of government since 2000.[16] The county has three branches: the executive, the legislative, and the judicial.[17] The executive branch consists of the County Executive, who is elected for a four-year term and serves as the chief executive officer of the county; and the County Manager, who is appointed by the County Executive and oversees the daily operations of the county departments.[17][18] The current County Executive isSara Innamorato, a Democrat who took office in 2024.[19] The current County Manager is William D. McKain, who was appointed by Fitzgerald in 2012 and reappointed in 2016 and 2020.[18] The legislative branch consists of the County Council, which is composed of 15 members elected for four-year terms from 13 single-member districts and 2At-Large representatives, currently occupied byBethany Hallam and Sam DeMarco. The council functions as the primary legislative and policy-making body of the county.[17][18] The current County Council President is Patrick Catena, a Democrat who represents District 4 and was elected by his fellow council members in 2018 and 2020.[18] The judicial branch consists of the Court of Common Pleas, which is the general trial court of the county; and the Magisterial District Courts, which are lower courts that handle minor criminal and civil cases. The judges of these courts are elected for ten-year terms.[17] The current President Judge of the Court of Common Pleas is Kimberly Berkeley Clark, who was elected by her fellow judges in 2018 for a five-year term.[17]
Allegheny County has 130 self-governing municipalities, the most in the state. These include one city (Pittsburgh), 96 boroughs, 30 townships, and two home rule municipalities (Bethel Park and McCandless).[20][21]Each municipality has its own elected officials, such as mayor, council, commissioners, supervisors, etc., and its own local services, such as police, fire, public works, etc.[20]Some municipalities also have their own municipal authorities that provide services such as water, sewer, transit, etc.[22]
There have been several proposals to consolidate or merge some of the municipalities in Allegheny County, either with each other or with the City of Pittsburgh, to reduce costs, improve efficiency, and enhance regional cooperation. However, none of these proposals have been implemented so far.[23][24] One of the most recent proposals is fromWilkinsburg, a borough that borders Pittsburgh and faces financial challenges due to declining population and tax base. In 2020, Wilkinsburg residents voted to approve a referendum to explore a merger with Pittsburgh. In 2021, a joint task force was formed to study the feasibility and impact of such a merger. The task force is expected to issue a report by June 2022. If both Wilkinsburg and Pittsburgh councils approve the merger, it would then need approval from the state legislature and governor before taking effect.[23] Another recent proposal is from Allegheny County Economic Development (ACED), which is seeking to enter into an agreement with a consultant to carry out historic preservation compliance activities for projects funded by various federal programs. The consultant would help ACED develop a Programmatic Memorandum of Agreement (PMOA) with the Pennsylvania State Historic Preservation Office (SHPO) and other stakeholders to streamline the review process for projects that may affect historic properties within the county. ACED issued a Request for Proposals (RFP) for this service in January 2022 and expects to select a consultant by March 2022.[25]
As of 19 May 2025,[update] there were 908,024 registered voters in the county; a majority were Democrats. There were 499,711 registeredDemocrats, 264,342 registeredRepublicans, 106,334 registered asindependents and 37,637 registered withother parties.[27]
TheRepublican Party had been historically dominant in county-level politics in the 19th and early 20th centuries; prior to theGreat Depression, Pittsburgh and Allegheny County had been majority Republican. Since the Great Depression on the state and national levels, theDemocratic Party has been dominant in county-level politics. It is by far the most Democratic county in western Pennsylvania. For much of the time between the Great Depression and the turn of the millennium, it was the second-strongest Democratic bastion in Pennsylvania, behind only Philadelphia.
In 2000, DemocratAl Gore won 56% of the vote and RepublicanGeorge W. Bush won 41%. In 2004, DemocratJohn Kerry received 57% of the vote and Republican Bush received 41%. In 2006, Democrats GovernorEd Rendell and SenatorBob Casey Jr. won 59% and 65% of the vote in Allegheny County, respectively. In 2008, DemocratBarack Obama received 57% of the vote, RepublicanJohn McCain received 41%, and each of the three state row office winners (Rob McCord for Treasurer,Jack Wagner for Auditor General, andTom Corbett for Attorney General) also carried Allegheny. In 2016, despiteDonald Trump being the first Republican to carry Pennsylvania since 1988,Hillary Clinton did slightly better than Barack Obama's 2012 vote total while Donald Trump was the worst performing Republican in 20 years. In the2018 Midterms, Democrats received an even higher percentage of the vote withTom Wolf and Casey receiving approximately two thirds of the county's vote.[28][29] This is an improvement over the approximately 55% each person received in the county in their last election in 2014 and 2012 respectively. In 2020, Joe Biden improved upon Clinton's performance, receiving the highest vote percentage for a Democrat sinceMichael Dukakis in 1988 and the most votes for a Democrat sinceLyndon B. Johnson in 1964.
In the 21st century, populist turns to the GOP from nearly all of Appalachia in general and western Pennsylvania in particular have left the county as one of the few in the region that still supports the Democrats at a high level.
As of the2010 census, there were 1,223,348 people living in the county. The population density was 1,676 people per square mile (647 people/km2). The racial makeup of the county was 82.87% White, 14.39% Black or African American, 2.94% Asian, 0.03% Pacific Islander, 0.37% from other races, and 1.40% from two or more races. About 1.31% of the population were Hispanic or Latino of any race.
At the2000 census,[40] there were 1,281,666 people, 537,150 households, and 332,495 families living in the county. The population density was 1,755 people per square mile (678 people/km2). There were 583,646 housing units at an average density of 799 per square mile (308/km2). The racial makeup of the county was 84.33% White, 12.41% Black or African American, 0.12% Native American, 1.69% Asian, 0.03% Pacific Islander, 0.34% from other races, and 1.07% from two or more races. About 0.87% of the population were Hispanic or Latino of any race. 20.0% were ofGerman, 15.0%Italian, 12.7%Irish, 7.5%Polish and 5.1% English ancestry. 93.5% spoke English and 1.3% Spanish as their first language.
There were 537,150 households, out of which 26.40% had children under the age of 18 living with them, 46.10% were married couples living together, 12.40% had a female householder with no husband present, and 38.10% were non-families. Some 32.70% of all households were made up of individuals, and 13.20% had someone living alone who was 65 years of age or older. The average household size was 2.31 and the average family size was 2.96.
The age distribution of the population shows 21.90% under the age of 18, 8.50% from 18 to 24, 28.30% from 25 to 44, 23.40% from 45 to 64, and 17.80% who were 65 years of age or older. The median age was 40. For every 100 females, there were 90.00 males; for every 100 females age 18 and over, there were 86.20 males.
In the late 18th century,farming played a critical role in the growth of the area. There was a surplus of grain due to transportation difficulties in linking with the eastern portion of the state. As a result, the farmers distilled the grain intowhiskey, which significantly helped the farmers financially.
Employment by occupation in Allegheny County
The area quickly became a key manufacturing area in the young nation. Coupled with deposits of iron and coal, and the easy access to waterways forbarge traffic, the city quickly became one of the most important steel producing areas in the world. Based on 2007 data from the US Army Corps of Engineers, Pittsburgh is the second (afterLaredo, Texas) busiest inland port in the nation.
US steel production declined late in the 20th century, and Allegheny County's economy began a shift to other industries. It is presently known for its hospitals, universities, and industrial centers. Despite the decline ofheavy industry, Pittsburgh is home to a number of major companies and is ranked in thetop ten among US cities hosting headquarters of Fortune 500 corporations, includingU.S. Steel Corporation,PNC Financial Services Group,PPG Industries, andH. J. Heinz Company.
TheThree Rivers Heritage Trail provides uninterrupted bicycle and pedestrian connections along the three rivers in the city, and theGreat Allegheny Passage trail runs from downtown Pittsburgh to Washington, D.C.
TheAllegheny County Airport is the original airport for Pittsburgh and houses a number of flight schools, charter flight operations, and medevac operations. It is owned and operated by The Allegheny County Airport Authority.
Pittsburgh International Airport is the major passenger airport for the county with service to many destinations on several airlines. Like the Allegheny County Airport, it is also owned and operated by The Allegheny County Airport Authority.
TheAllegheny Land Trust, a regional land conservation organization based inSewickley, has acquired and preserved parcels of land throughout the county for use as scenic and recreational green space.[44][45] In 2012, the trust pursued the purchase of land formerly owned by the Pittsburgh Cut Flower Company inRichland Township.[46] In 2020, it received a grant to convert the former Churchill Valley Country Club into public green space.[47][48] Later that year, it donated 20 undeveloped acres across three parcels inHampton to expandNorth Park.[49]
A 2025 economic impact study commissioned by the Allegheny County Parks Foundation found that the county's nine regional parks, including North Park andSouth Park, collectively support tourism, raise surrounding property values, and provide environmental benefits such as carbon storage and urban tree canopy, generating millions of dollars in value annually.[50]
Map of Allegheny County, Pennsylvania, with municipal labels showing cities and boroughs (red), Townships (white), and census-designated places (blue)
Under Pennsylvania law, there are four types of incorporated municipalities:cities,boroughs,townships, and (in a case) atown. The following municipalities are in Allegheny County:
Census-designated places are geographical areas designated by theUS Census Bureau for the purposes of compiling demographic data. They are not actual jurisdictions under Pennsylvania law. Other unincorporated communities, such as villages, may be listed here as well.
Carrick Borough – now the neighborhood of Carrick. Formed out of Baldwin Township in 1904, this borough existed until it was annexed by Pittsburgh in 1927. It was named for Carrick-on-Suir, Ireland. Some of the area'smanhole covers still bear the Carrick Borough name.
Chartier Township – existed at the time of the 1860 U.S. Federal Census.[54]
Collins Township – in what is now the northeast part of the City of Pittsburgh, east of Lawrenceville and north ofPenn Avenue.
Knoxville Borough
Lawrenceville Borough
McClure Township – McClure was formed in 1858 from the section of Ross Township adjacent to Allegheny City. In 1867 McClure, along with sections of Reserve Township, was incorporated into Allegheny City. The McClure section of this annexation became Wards 9 (Woods Run Area) and 11 (present-day Brighton Heights) in the City of Pittsburgh.
Mifflin Township- comprised the modern day communities of Whitaker, West Mifflin, West Homestead, West Elizabeth, Pleasant Hills, Munhall, Lincoln Place, Jefferson Hills, Homestead, Hays, Duquesne, Dravosburg, Clairton and part of Baldwin.[55]
Patton Township – was in the east-central part of the county, north of North Versailles Township, east of Wilkins and Penn Townships, and south of Plum Township. In the U.S. census for 1860–1880. In 1951 it became incorporated as the borough ofMonroeville.
Northern Liberties Borough – in what is now theStrip District of Pittsburgh. The borough was annexed to Pittsburgh in 1837 as the first addition to the city's original territory.
Peebles Township – included most of what is now the eastern part of the city of Pittsburgh from the Monongahela River in the south (today'sHazelwood) to the Allegheny River in the north. It was subdivided into Collins andLiberty townships, all of which were incorporated into Pittsburgh in 1868.
St. Clair Township – stretched from the Monongahela River south to the Washington County line. It divided intoLower St. Clair, which eventually became part of the City of Pittsburgh, Dormont, Mount Lebanon, and Upper St. Clair.
Snowden – now known as South Park Township.
Sterrett Township
Temperanceville – what is now Pittsburgh's West End.
Union Borough – the area surrounding Temperanceville.
West Liberty Borough – now the neighborhoods of Brookline and Beechview in Pittsburgh.
^Includes Allegheny, Washington, Butler, Beaver, Lawrence and Armstrong Counties
^Mean monthly maxima and minima (i.e. the highest and lowest temperature readings during an entire month or year) calculated based on data at said location from 1991 to 2020.
^Records kept September 1874 to June 1935 at the Weather Bureau Office across the Allegheny River fromdowntown, atAllegheny County Airport from July 1935 to 14 September 1952, and at Pittsburgh Int'l (KPIT) since 15 September 1952. Due to its river valley and urban location as well as elevation, many of the summertime warm minima temperature records set at the WBO have not even come close to being matched at KPIT, which is at-elevation and located in the western suburbs. For more information, seeThreadex
^"PHMC Historical Markers Search".Pennsylvania Historical and Museum Commission. Commonwealth of Pennsylvania. Archived fromthe original(Searchable database) on March 21, 2016. RetrievedJanuary 25, 2014.
^"Find a County". National Association of Counties. Archived fromthe original on May 31, 2011. RetrievedJune 7, 2011.
^Kussart, Mrs. S. (April 24, 1930)."Navigation on the Monongahela River". The Daily Republican (Monongahela, Pennsylvania). p. 3. RetrievedAugust 10, 2018.
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