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County · code 17163

St. Clair CountyIllinois

St. Clair County is located in Illinois and has its county seat in Belleville. The county was created on April 27, 1790, by the Northwest Territory and named after Arthur St. Clair.

  • Founded1790
  • County seatBelleville
  • Named forArthur St. Clair
  • Land area658 sq mi + 16 sq mi water
  • Population257,400 2020 Census
  • Parcels mapped147,941 checked 15 October 2026
Open the free map Click any parcel in St. Clair County: acreage, parcel id, address and who publishes the map. No sign-in.

Updated

MonroeSt. Louis city, MOMadisonClintonWashingtonSt. Louis, MO Belleville Census outline · seat marked

Where it is

St. Clair on the map of Illinois

Illinois has 102 counties and county equivalents, each with its own records office. Shapes with a page are links.

Adams CountyAlexander CountyBond CountyBoone CountyBrown CountyBureau CountyCalhoun CountyCarroll CountyCass CountyChampaign CountyChristian CountyClark CountyClay CountyClinton CountyColes CountyCook CountyCrawford CountyCumberland CountyDeKalb CountyDe Witt CountyDouglas CountyDuPage CountyEdgar CountyEdwards CountyEffingham CountyFayette CountyFord CountyFranklin CountyFulton CountyGallatin CountyGreene CountyGrundy CountyHamilton CountyHancock CountyHardin CountyHenderson CountyHenry CountyIroquois CountyJackson CountyJasper CountyJefferson CountyJersey CountyJo Daviess CountyJohnson CountyKane CountyKankakee CountyKendall CountyKnox CountyLake CountyLaSalle CountyLawrence CountyLee CountyLivingston CountyLogan CountyMcDonough CountyMcHenry CountyMcLean CountyMacon CountyMacoupin CountyMadison CountyMarion CountyMarshall CountyMason CountyMassac CountyMenard CountyMercer CountyMonroe CountyMontgomery CountyMorgan CountyMoultrie CountyOgle CountyPeoria CountyPerry CountyPiatt CountyPike CountyPope CountyPulaski CountyPutnam CountyRandolph CountyRichland CountyRock Island CountySaline CountySangamon CountySchuyler CountyScott CountyShelby CountyStark CountyStephenson CountyTazewell CountyUnion CountyVermilion CountyWabash CountyWarren CountyWashington CountyWayne CountyWhite CountyWhiteside CountyWill CountyWilliamson CountyWinnebago CountyWoodford CountySt. Clair County St. Clair
Counties of Illinois · St. Clair highlighted

History

Founded in 1790

An old deed may name a county that no longer exists, or a boundary that has since moved.

St. Clair County was created by the Northwest Territory on April 27, 1790, from non-county area. Between 1800 and 1809, the county passed through Indiana Territory before becoming part of Illinois Territory on March 1, 1809.

Boundary changes from the Newberry Library, Atlas of Historical County Boundaries; the 5 that matter most are shown first.

  1. 1790
    St. Clair County created St. Clair created by the Northwest Territory from non-county area. · Terr. Papers U.S., 3:301-303
  2. 1800
    Became part of Illinois St. Clair became a county in Indiana Territory when Indiana Territory was created from the Northwest Territory. · Terr. Papers U.S., 3:86-88; U.S. Stat., vol. 2, ch. 41 [1800]/pp. 58-59
  3. 1809
    St. Clair County created St. Clair became part of Illinois Territory when Illinois Territory was created from Indiana Territory; St. Clair continued de facto, with no new boundaries specified. · U.S. Stat., vol. 2, ch 13 [1809], sec. 1/pp. 514-515
  4. 1809
    St. Clair County created St. Clair created by Illinois Territory, effectively continuing the county of the same name created by the Northwest Territory in 1790. St. Clair exchanged with Indiana Territory, and lost to Randolph; St. Clair eliminated from present Indiana.
    from Randolph
    · Ill. Terr. Recs., 3-4; Terr. Papers U.S., 17:620-621
  5. 1818
    Became part of Illinois St. Clair became a county in the state of Illinois when Illinois was created from Illinois Territory. · Terr. Papers U.S., 10:803; U.S. Stat., vol. 3, ch. 67 [1818], secs. 1-2, 7/pp. 428-429, 431, and res. 1 [1818]/p. 536
Show all 16 changes (11 more)
  1. 1790
    St. Clair County created St. Clair created by the Northwest Territory from non-county area. · Terr. Papers U.S., 3:301-303
  2. 1795
    Lost territory St. Clair lost to creation of Randolph.
    to Randolph
    · Terr. Papers U.S., 3:441
  3. 1800
    Became part of Illinois St. Clair became a county in Indiana Territory when Indiana Territory was created from the Northwest Territory. · Terr. Papers U.S., 3:86-88; U.S. Stat., vol. 2, ch. 41 [1800]/pp. 58-59
  4. 1801
    Gained territory St. Clair gained from Knox (Indiana) and non-county area in present Illinois, Indiana, Michigan, Minnesota, and Wisconsin; St. Clair lost to Randolph.
    from Knox (Ind.)from Randolph
    · Ind. Terr., Exec. Journal, 97-100; Pence and Armstrong, 212, 520
  5. 1803
    Lost territory St. Clair lost to creation of Wayne (Indiana Territory, extinct).
    to Wayne
    · Ind. Terr., Exec. Journal, 114-115; Pence and Armstrong, 218; U.S. Stat., vol. 2, ch. 40 [1802], secs. 1-3/pp. 173-174; Van Zandt, 112
  6. 1803
    Exchanged territory St. Clair exchanged with Randolph.
    with Randolph
    · Ind. Terr., Exec. Journal, 117-118
  7. 1809
    St. Clair County created St. Clair became part of Illinois Territory when Illinois Territory was created from Indiana Territory; St. Clair continued de facto, with no new boundaries specified. · U.S. Stat., vol. 2, ch 13 [1809], sec. 1/pp. 514-515
  8. 1809
    St. Clair County created St. Clair created by Illinois Territory, effectively continuing the county of the same name created by the Northwest Territory in 1790. St. Clair exchanged with Indiana Territory, and lost to Randolph; St. Clair eliminated from present Indiana.
    from Randolph
    · Ill. Terr. Recs., 3-4; Terr. Papers U.S., 17:620-621
  9. 1812
    Lost territory St. Clair lost to creation of Madison; St. Clair eliminated from present Michigan, Minnesota, and Wisconsin.
    to Madison
    · Ill. Terr. Recs., 26; Terr. Papers U.S., 17:643
  10. 1813
    Exchanged territory St. Clair exchanged with Randolph.
    with Randolph
    · Ill. Terr. Laws, 120-121
  11. 1816
    Lost territory St. Clair lost to creation of Monroe.
    to Monroe
    · Ill. Terr. Laws, 195-198
  12. 1818
    Lost territory St. Clair lost to creation of Washington.
    to Washington
    · Ill. Terr. Laws, 312-314
  13. 1818
    Boundary clarified Boundary between St. Clair and Madison was redefined (no change).
    with Madisonno change
    · Ill. Terr. Laws, 311
  14. 1818
    Became part of Illinois St. Clair became a county in the state of Illinois when Illinois was created from Illinois Territory. · Terr. Papers U.S., 10:803; U.S. Stat., vol. 3, ch. 67 [1818], secs. 1-2, 7/pp. 428-429, 431, and res. 1 [1818]/p. 536
  15. 1825
    Lost territory St. Clair lost to Monroe.
    to Monroe
    · Ill. Laws 1824-1825, pp. 109-110
  16. 1827
    Lost territory St. Clair lost to Monroe.
    to Monroe
    · Ill. Laws 1826-1827, pp. 7-8

Land and parcels

What the maps cover in St. Clair

Who publishes each layer, how good it is, and when we last checked.

Official
from the office that keeps the record
Good enough
a reliable statewide or national copy
Fallback
a guide only; check the official record
Missing
nothing public found yet

People and land

St. Clair by the Census

Population
257,400 2020 Census count
Housing units
114,595 2020 Census count
Land area
658 square miles
Water area
16 square miles
People per sq mi
391 population ÷ land area

Source: US Census Bureau, 2020 Census; US Census Bureau, 2020 Gazetteer Files. Not endorsed or certified by the Census Bureau.

Rules and offices

Who to ask before you build, dig or sell

Official county pages only. We link to them; we do not copy them, because they change.

Inside a city or town, permits usually come from that city rather than the county.

Records

Permits

Zoning and code

GIS and maps

County government

See your own lot on these maps

Open St. Clair County on Parcel Chart's free map and click your parcel. Save it with a free account; the full record of your place (site map, projects, documents) is Pro, in early access.

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Questions

Common questions about St. Clair County

When was St. Clair County founded?
St. Clair County was founded in 1790, and named after Arthur St. Clair.
What is the county seat of St. Clair County?
The county seat of St. Clair County is Belleville.
Is there an online parcel map for St. Clair County?
Yes. St. Clair County publishes a parcel map of 147,941 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.
Has St. Clair County's boundary or name changed?
St. Clair County was created in 1790. Since then the Atlas of Historical County Boundaries records 14 later changes, chiefly involving Randolph County, Monroe County and Knox (Ind.) County.
Who issues building permits in St. Clair County?
The county's page on building permits: Building Permits. Inside a city or town, ask that city first.
Is my lot in a flood zone?
We do not have flood maps for St. Clair County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.

Nearby

Counties next door