The county seat was first established atHenderson. A courthouse was built there and placed into service in 1879. It was used in that capacity until 1915, when the county seat was moved to Gaylord (after Gaylord residents presented a petition to county supervisors). Now the Henderson Community Building, the original courthouse presently houses Henderson City offices.[5]
TheMinnesota River flows northeastward along Sibley County's eastern border. It is fed by theRush River, whose three branches drain the lower part of the county before merging and then meeting the Minnesota belowHenderson.Bevens Creek drains the upper part of the county, flowing northeastward intoCarver County. The county terrain consists of rolling hills etched with drainages and dotted with lakes and ponds, with the area devoted to agriculture.[6] The terrain slopes to the east and north, with its highest point near its northwest corner at 1,083 ft (330 m) ASL.[7] The county has an area of 601 square miles (1,560 km2), of which 589 square miles (1,530 km2) is land and 12 square miles (31 km2) (2.0%) is water.[8] Most of theRush River'swatershed is in Sibley County.
As of thecensus of 2000, there were 15,356 people, 5,772 households, and 4,086 families in the county. Thepopulation density was 26.1 per square mile (10.1/km2). There were 6,024 housing units at an average density of 10.2 per square mile (3.9/km2). The racial makeup of the county was 95.57%White, 0.12%Black orAfrican American, 0.26%Native American, 0.33%Asian, 3.09% fromother races, and 0.62% from two or more races. 5.43% of the population wereHispanic orLatino of any race. 65.7% were ofGerman and 6.3%Norwegian ancestry.
There were 5,772 households, of which 33.6% had children under 18 living with them, 61.1% weremarried couples living together, 5.8% had a female householder with no husband present, and 29.2% were non-families. 25.4% of all households were made up of individuals, and 13.0% had someone living alone who was 65 or older. The average household size was 2.60 and the average family size was 3.14.
The county population was 27.7% under 18, 7.5% from 18 to 24, 27.1% from 25 to 44, 21.3% from 45 to 64, and 16.4% 65 or older. The median age was 37. For every 100 females there were 102.9 males. For every 100 females 18 and over, there were 99.9 males.
The median income for a household in the county was $41,458, and the median income for a family was $48,923. Males had a median income of $31,002 versus $22,527 for females. Theper capita income was $18,004. About 5.1% of families and 8.1% of the population were below thepoverty line, including 9.8% of those under 18 and 7.8% of those 65 or over.