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Background • Federal Census Summary • State Map with County Boundaries • Counties • Links to State Resources Background
Illinois was included in the Northwest Territory established in 1787 and then in Indiana Territory (1800). Illinois Territory was established in 1809, and included virtually all of present-day Wisconsin and portions of Minnesota and the Upper Peninsula of Michigan. Illinois was admitted as a State on December 3, 1818 with essentially its present boundaries.
| Capital: Springfield | Total Area: 57,918 sq mi | ||
| Latitude: 36°58'N to 42°30'N | Longitude: 87°30'W to 91°30'W | ||
| Last Significant Boundary Change: 1820 | |||
In 1790 the Northwest Territory had no census coverage. The population shown for 1800 is the total of two counties and one community in present-day Illinois, at that time part of Indiana Territory. Knox County, Indiana Territory, also included some population in what is now Illinois. In 1810, the returns for the two counties of Illinois Territory included some settlements in present-day Wisconsin. The northern part of the State was not fully covered by the census until 1830.
| 1790: --- | 1800: 2,458 | 1810: 12,282 | 1820: 55,211 |
| 1830: 157,445 | 1840: 476,183 | 1850: 851,470 | 1860: 1,711,951 |
| 1870: 2,539,891 | 1880: 3,077,871 | 1890: 3,826,352 | 1900: 4,821,550 |
| 1910: 5,638,591 | 1920: 6,485,280 | 1930: 7,630,654 | 1940: 7,897,241 |
| 1950: 8,712,176 | 1960: 10,081,158 | 1970: 11,113,976 | 1980: 11,426,518 |
| 1990: 11,430,602 | 2000: 12,419,293 |