Counties in Illinois
Each county page says how cases move there under Illinois's rules, and lists the police agencies that serve it.
102 counties, largest first
- Cook County5,194,625 people · 178 agencies
- DuPage County934,298 people · 42 agencies
- Lake County719,339 people · 48 agencies
- Will County712,253 people · 43 agencies
- Kane County525,757 people · 32 agencies
- McHenry County317,751 people · 31 agencies
- Winnebago County283,674 people · 19 agencies
- Madison County263,110 people · 34 agencies
- St. Clair County250,708 people · 34 agencies
- Champaign County209,972 people · 16 agencies
- Sangamon County194,170 people · 31 agencies
- Peoria County178,553 people · 14 agencies
- McLean County171,419 people · 17 agencies
- Kendall County145,470 people · 10 agencies
- Rock Island County141,869 people · 17 agencies
- Tazewell County130,049 people · 21 agencies
- LaSalle County107,773 people · 19 agencies
- Kankakee County105,525 people · 15 agencies
- DeKalb County101,835 people · 14 agencies
- Macon County99,300 people · 13 agencies
- Vermilion County71,259 people · 18 agencies
- Williamson County67,225 people · 10 agencies
- Adams County64,267 people · 6 agencies
- Whiteside County54,121 people · 11 agencies
- Grundy County54,052 people · 12 agencies
- Boone County53,568 people · 4 agencies
- Jackson County52,501 people · 9 agencies
- Ogle County51,399 people · 10 agencies
- Henry County48,095 people · 13 agencies
- Knox County47,767 people · 7 agencies
- Coles County46,607 people · 7 agencies
- Macoupin County43,748 people · 12 agencies
- Stephenson County43,220 people · 8 agencies
- Woodford County38,111 people · 12 agencies
- Clinton County37,128 people · 12 agencies
- Franklin County36,916 people · 10 agencies
- Marion County36,382 people · 8 agencies
- Jefferson County36,147 people · 5 agencies
- Livingston County35,057 people · 6 agencies
- Monroe County34,840 people · 5 agencies
- Effingham County34,519 people · 6 agencies
- Christian County33,443 people · 10 agencies
- Lee County32,914 people · 5 agencies
- Fulton County32,901 people · 11 agencies
- Morgan County32,515 people · 6 agencies
- Bureau County32,510 people · 12 agencies
- Randolph County29,921 people · 10 agencies
- Montgomery County28,076 people · 12 agencies
- Logan County27,182 people · 5 agencies
- Iroquois County26,150 people · 10 agencies
- McDonough County25,916 people · 8 agencies
- Saline County22,772 people · 5 agencies
- Jo Daviess County21,594 people · 8 agencies
- Jersey County21,160 people · 5 agencies
- Fayette County20,790 people · 6 agencies
- Shelby County20,576 people · 6 agencies
- Perry County20,160 people · 7 agencies
- Douglas County19,880 people · 7 agencies
- Crawford County18,648 people · 5 agencies
- Bond County16,959 people · 6 agencies
- Hancock County16,803 people · 9 agencies
- Piatt County16,791 people · 6 agencies
- Union County16,656 people · 5 agencies
- Edgar County16,323 people · 4 agencies
- Warren County16,222 people · 4 agencies
- Wayne County15,882 people · 3 agencies
- Carroll County15,419 people · 8 agencies
- Mercer County15,229 people · 5 agencies
- Richland County15,219 people · 2 agencies
- De Witt County15,118 people · 3 agencies
- Clark County15,114 people · 5 agencies
- Moultrie County14,371 people · 5 agencies
- Pike County14,231 people · 4 agencies
- Lawrence County13,790 people · 5 agencies
- Washington County13,564 people · 7 agencies
- Massac County13,502 people · 3 agencies
- Johnson County13,363 people · 3 agencies
- White County13,250 people · 6 agencies
- Ford County13,216 people · 4 agencies
- Clay County12,793 people · 2 agencies
- Cass County12,463 people · 5 agencies
- Mason County12,411 people · 8 agencies
- Menard County11,863 people · 4 agencies
- Marshall County11,473 people · 6 agencies
- Greene County11,313 people · 5 agencies
- Wabash County10,907 people · 2 agencies
- Cumberland County10,208 people · 4 agencies
- Jasper County9,032 people · 2 agencies
- Hamilton County7,859 people · 2 agencies
- Schuyler County6,657 people · 2 agencies
- Brown County6,401 people · 2 agencies
- Henderson County5,984 people · 5 agencies
- Edwards County5,898 people · 4 agencies
- Putnam County5,619 people · 4 agencies
- Stark County5,319 people · 4 agencies
- Scott County4,866 people · 3 agencies
- Pulaski County4,820 people · 4 agencies
- Gallatin County4,616 people · 5 agencies
- Alexander County4,570 people · 2 agencies
- Calhoun County4,300 people · 2 agencies
- Pope County3,672 people · 2 agencies
- Hardin County3,588 people · 2 agencies
Population: Census Bureau county population estimates, Vintage 2025 (cc-est2025-alldata), July 1, 2025.