The city ofChicago is divided into 77community areas for statistical and planning purposes.Census data and other statistics are tied to the areas, which serve as the basis for a variety ofurban planning initiatives on both the local and regional levels. The areas' boundaries do not generally change, allowing comparisons of statistics across time. The areas are distinct from but related to the more numerousneighborhoods of Chicago; an area often corresponds to a neighborhood or encompasses several neighborhoods, but the areas do not always correspond to popular conceptions of the neighborhoods due to a number of factors including historical evolution and choices made by the creators of the areas. As of 2020^[update],Near North Side is the most populous of the areas with over 105,000 residents, whileBurnside is the least populous with just over 2,500. Other geographical divisions of Chicago exist, such as the "sides" with origin in the 3 branches of theChicago River, the 50 wards of theChicago City Council which undergo redistricting based in population movements, and the parishes of the Roman Catholic Church.

The Social Science Research Committee at theUniversity of Chicago defined the community areas in the 1920s based on neighborhoods or groups of related neighborhoods within the city. In this effort it was led by sociologistsRobert E. Park andErnest Burgess, who believed that physical contingencies created areas that would inevitably form a common identity. Except for the addition of two areas (O'Hare from land annexed by the city in 1956 andEdgewater's separation fromUptown in 1980) and peripheral expansions due to minor annexations, the areas' boundaries have never been revised to reflect change but instead have been kept stable. The areas have become a part of the culture of Chicago, contributing to its perception as a "city of neighborhoods" and breaking it down into smaller regions for easier analysis and local planning. Nevertheless, Park's and Burgess's ideas on the inevitability of physically related areas forming a common bond have been questioned, and the unchanging nature of the areas has at times been seen as analytically problematic with major subsequent changes in some of the areas' urban landscapes, such as the construction of expressways.

During the 19th centurywards were used by theCensus Bureau for data at the level below cities.^[1] This was problematic as wards were political subdivisions and thus changed after each census, limiting their utility for comparisons over time.^[1]Census tracts were first used in Chicago in the1910 Census.^[1] However, by the 1920s the Social Science Research Committee at theUniversity of Chicago wanted divisions that were more natural and manageable than the arbitrarily-designated and numerous census tracts.^[1][2] The sociologistRobert E. Park led this charge, considering physical barriers such as railroads and theChicago River to form distinctive and consistent areas within the city,^[1] which he deemed "natural" areas that would eventually merge into a distinctive identity.^[1][2]Ernest Burgess, a colleague of Park's who shared his thinking, was crucial in creating and naming the community areas.^[2] Initially able to identify 400 neighborhoods of the city, he considered that number excessive and trimmed it down to 80 and thereafter 75 by grouping related neighborhoods into a single community area.^[2] The Chicago Department of Public Health wished to present local differences in birth and death rates; it worked with the committee to produce the list of 75 community areas, which were divided into 935 census tracts.^[1]

After the community areas were introduced, theUniversity of Chicago Press published data sorted by them from the1920 and1930 Censuses,^[1] as well as a citywide 1934 census to help collect data related to theGreat Depression,^[2] in what was known as theLocal Community Fact Book.^[1] With the exception of1970 (whose data was published in 1980^[2]), it continued this publication for every subsequent census through 1990, expanding in the 1960s to also cover major suburbs of Chicago.^[2][3] TheChicago Metropolitan Agency for Planning continues this work by periodically publishing "Community Snapshots" of the community areas and suburbs, the most recent being data from 2018 published in June 2020^[update].^[4]

Only two major changes have occurred in the boundaries of the community areas.^[1]O'Hare was created from land that was annexed by Chicago in 1956 to controlO'Hare International Airport.^[a][5]Edgewater was separated fromUptown in 1980 as residents considered being joined to it a detriment to obtaining aid for local improvements.^[6] In addition to these two there have been minor changes due to further annexations and additions to theLake Michigan shoreline.^[1][7]

The areas are used for statistical and planning purposes by such professions as assessors, charities, and reporters.^[2] Shortly after their development they were used for all kinds of statistics, including movie theater distribution and juvenile delinquency.^[2] Although developed by the University of Chicago, they have been used by other universities in the Chicago area, as well as by the city and regional planners.^[2] They have contributed to Chicago's reputation as the "city of neighborhoods", and are argued to break up an intimidating city into more manageable pieces.^[2] Chicago was an early adopter of such a system, and as of 1997^[update] most cities in the United States still lacked analogous divisions.^[2]

The areas do not necessarily correspond to popular imagination of the neighborhoods.^[1] For example, the Pilsen and Back of the Yards neighborhoods are much better known than their respective community areasLower West Side andNew City.^[1] In the case of New City this was a deliberate choice; Burgess opted for the less common "New City" to name the area as "Back of the Yards" carried a stigma after the publication ofUpton Sinclair'sThe Jungle (1904), which made the area notorious for its poor living conditions.^[2] Some of these discrepancies are due to names that were common at the time of the adoption of community areas but have since been supplanted by others.^[2] The static nature of area boundaries is one of their benefits, but is also problematic at times such as when expressways were built in the mid-20th century and divided neighborhoods without area boundaries adapting.^[1] The concept of a "natural area" that underpinned Park's and Burgess's thinking has also been challenged.^[1]

Chicago is traditionally divided into the three "sides" of the North Side,West Side, andSouth Side by theChicago River. These three sides are represented by the white stripes on theFlag of Chicago.^[13] The city is also divided into 50 wards for the purpose ofelecting one alderman each to theChicago City Council. These wards have at times generated identities similar to neighborhoods. Unlike community areas, wards are adjusted decennially to account for population shifts.^[14] Another method of neighborhood nomenclature in heavily Catholic neighborhoods of Chicago has been to refer to communities in terms ofparishes.^[2] For example, one might say, "I live in St. Gertrude's, but he is from Saint Ita's."^[2]

• Community Area 2000 and 2010 Census Population ComparisonsArchived August 25, 2012, at theWayback Machine
• Community Areas Map (downloadable in common GIS formats) on City of Chicago Data Portal

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