How this list was compiled: Items made on 2026-09-26. Licence: public domain (work of the United States government, 17 U.S.C. 105): https://www2.census.gov/geo/pdfs/maps-data/data/tiger/tgrshp2023/TGRSHP2023_TechDoc_Ch1.pdf
The drawing: Drawn for this site from U.S. Census Bureau 2023 cartographic boundary file cb_2023_us_county_5m (scale 1:5,000,000), https://www2.census.gov/geo/tiger/GENZ2023/shp/cb_2023_us_county_5m.zip, downloaded 2026-09-19. Surrounding land from U.S. Census Bureau 2023 cartographic boundary file cb_2023_us_state_5m (scale 1:5,000,000), https://www2.census.gov/geo/tiger/GENZ2023/shp/cb_2023_us_state_5m.zip, downloaded 2026-09-19. Albers equal-area conic projection, central meridian 89.3°W, standard parallels 37.9°N and 41.6°N. Outlines simplified; small islands are left out. Licence: public domain (work of the United States government, 17 U.S.C. 105): https://www2.census.gov/geo/pdfs/maps-data/data/tiger/tgrshp2023/TGRSHP2023_TechDoc_Ch1.pdf
How it works
This Illinois counties map quiz names a county, Cook or Sangamon or Jo Daviess, and you tap it on a blank map. All 102 are here, in three sets that run from the Wisconsin line to the southern tip.
Read the full guide
Names you know from next door
Illinois shares 43 county names with Indiana, 42 with Kentucky, 41 with Missouri, 33 with Iowa and 11 with Wisconsin, so a name alone may bring another state's map to mind. Thirty-eight names are in none of the five neighbors, Cook, Sangamon, Peoria and Kankakee among them.
Near twins on the map
De Witt and DeKalb are two counties, one in the middle of the state and one in the north. If you type a name, Saint Clair is taken for St. Clair, and Jo Daviess is as good as Jo Daviess County.
Springfield, the capital, is in Sangamon County, near the middle of the map.
Questions and answers
What is the smallest county in Illinois?
Putnam County, by land area, and it is the smallest shape on this map too. McLean County is the largest on both counts.
Which Illinois county has the fewest people?
Hardin County, with about 3,600 people in the Census Bureau's estimate for 2025. Cook County has the most, a little over five million.
Is it DeKalb or De Kalb, LaSalle or La Salle?
The quiz follows the Census Bureau's county list: DeKalb, DuPage and LaSalle are written as one word, and De Witt, Jo Daviess, Rock Island and St. Clair as two.
Which Illinois county names are in every neighboring state?
Four: Jackson, Jefferson, Monroe and Washington are county names in Illinois and in Indiana, Iowa, Kentucky, Missouri and Wisconsin. On this map each one is the Illinois county.