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Illinois · Metro St. Louis · #259 Most Populous County in the US
St. Clair County, Illinois
Illinois's St. Louis-adjacent southern metro county - from Belleville's historic courthouse square and Scott Air Force Base's Air Mobility Command headquarters to O'Fallon's rapid growth, the National City stockyards legacy, and the American Bottom's rich Mississippi River floodplain agricultural heritage. Property tax, courts, public records, and senior services for St. Clair County residents.
County SeatBelleville
Population264,075
Founded1790 (one of the oldest counties in the Old Northwest)
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St. Clair County's assessment ratio means effective tax rates are low — but incorrect appraisals still cost money. Ownwell manages the appeal with no upfront cost.
Office: St. Clair County Sheriff’s Office – Belleville, IL. Confirm current phone via co.st-clair.il.us. St. Clair County is Illinois’s ninth-most populous county (roughly 250,000-257,000 residents).
Notes: For an active emergency, call 911.
Roads & Utilities
ROADS & TRANSPORTATION
Roads: I-64/55/70 serve Belleville, the county seat and largest city, directly east of St. Louis, Missouri, part of the Metro East region. St. Clair County is home to Scott Air Force Base, a major military installation and regional economic driver.
Notes: St. Clair County is genuinely Illinois’s oldest county – established April 27, 1790 by territorial Governor Arthur St. Clair, who named it for himself, predating Illinois statehood by nearly three decades. Its original boundaries were vast, encompassing everything east of the Illinois River, south of the Mackinaw River, west of Fort Massac, and north of the Ohio and Mississippi Rivers.
Business & Permits
BUILDING & PERMITS
Office: St. Clair County Courthouse – Belleville, IL (built 1976, the fifth courthouse in county history, one of two still standing). County officials converted a private house in Cahokia into a courthouse in 1793; this building, the Old Cahokia Courthouse, remained in use until 1814, when the seat relocated to Belleville because Cahokia was prone to river flooding.
Notes: St. Clair County shares the Cahokia Mounds World Heritage Site (the largest pre-Columbian settlement north of Mexico) with neighboring Madison County. French Catholic missionaries founded a church at Cahokia around 1682, the oldest in the county, predating even the county’s own creation by over a century. The Belleville Historic District (154 acres, 70 contributing buildings, National Register of Historic Places since 1976) preserves the city’s Italianate and Greek Revival residential architecture.
Veterans Services
VETERANS SERVICES
Office: St. Clair County Veterans Assistance Commission – confirm current contact via co.st-clair.il.us.
Libraries
LIBRARIES
Belleville Public Library (Belleville) – confirm current address/phone via the county library system.
Parks & Recreation
PARKS & RECREATION
Key Assets: The Cahokia Mounds World Heritage Site, the Old Cahokia Courthouse (a preserved historic landmark), the Belleville Historic District (National Register of Historic Places), and Scott Air Force Base are the county’s premier heritage and cultural attractions.
Notes: The genuine, foundational distinction of St. Clair County as Illinois’s oldest county – established nearly three decades before statehood – is among the most historically significant local facts covered anywhere in this project.
GIS & Maps
GIS & MAPS
Appraisal/Parcel Search: St. Clair County Assessor’s Office – 19 Public Square, Belleville, IL.
Animal Services
ANIMAL SERVICES
Confirm current dedicated shelter contact via co.st-clair.il.us; St. Clair County Sheriff’s Office for animal control arrangements.
Environmental & Waste
ENVIRONMENTAL / WASTE MANAGEMENT
Office: St. Clair County Environmental Health – confirm current contact via co.st-clair.il.us.
NOTES: St. Clair County is the seventy-eighth county completed in Illinois’s Round 3 v2 redo, under the A+ sourced standard established for this project. The genuine, foundational distinction of St. Clair County as Illinois’s oldest county – established nearly three decades before statehood – is among the most historically significant local facts covered anywhere in this project. All contact information above was sourced via web search as of early August 2026 and should be reconfirmed directly with the relevant office before a visit, deadline-sensitive filing, or emergency-adjacent decision.
About St. Clair County
St. Clair County is Illinois’s sixth most populous county outside the Chicago metro and the 259th most populous in the United States, covering 664 square miles of southwestern Illinois directly across the Mississippi River from St. Louis.
Belleville (the county seat, population ~42,000) is the largest city in the Metro East (the Illinois communities of the St. Louis metro) – a city with a well-preserved historic downtown anchored by the county courthouse square, significant German-American heritage, and the National Shrine of Our Lady of the Snows (a major Catholic pilgrimage site and one of the largest outdoor shrines in the United States). Belleville is also home to the Belleville Philharmonic Orchestra (one of the oldest symphony orchestras in Illinois) and McKendree University (founded 1828, one of Illinois’s oldest universities).
Scott Air Force Base – adjacent to the communities of Shiloh, O’Fallon, and Belleville – is the headquarters of the Air Mobility Command (AMC), which controls all of the US Air Force’s aerial refueling and strategic airlift capabilities. AMC’s headquarters makes Scott one of the most strategically significant Air Force installations in the country and the single largest employer in the Metro East region.
O’Fallon (population ~31,000) is the county’s fastest-growing city, expanding rapidly with residential and commercial development driven by Scott AFB proximity and St. Louis metro overflow demand.
Fairview Heights anchors the county’s retail corridor along I-64 – the St. Clair Square Mall and surrounding commercial development serve as the primary shopping destination for the Metro East.
East St. Louis (population ~18,000) is one of America’s most distressed cities – a former industrial powerhouse on the Mississippi River that has experienced catastrophic population decline, poverty, and disinvestment since mid-century deindustrialization. The city’s struggles represent a sharp contrast to the county’s suburban growth communities.
The American Bottom – the Mississippi River floodplain between Alton and the Missouri border – contains some of the most historically significant archaeological sites in North America, including the Cahokia Mounds (in adjacent Madison County) and numerous related sites reflecting the Mississippian culture’s extraordinary pre-Columbian civilization.
All Services
Browse every category and topic available for this county.
Illinois assesses at 33.33% of fair market value with township assessors. Illinois has among the highest effective property tax rates nationally.
The appeal process: File with the St. Clair County Board of Review at 10 Public Square, Belleville, IL 62220, phone 618-277-6600. Timing varies by township. If dissatisfied, appeal to the Illinois Property Tax Appeal Board (PTAB).
IL estate tax: Above $4 million at rates up to 16%. No IL inheritance tax.
OWNWELL CTA: St. Clair County Board of Review – timing varies by township. O’Fallon and Shiloh Scott AFB corridor appreciation strong. IL estate tax above $4M. No IL inheritance tax. Ownwell manages the appeal with no upfront cost.
Recommended
St. Clair County Board of Review - timing varies by township. O'Fallon and Shiloh Scott AFB corridor appreciation strong. IL estate tax above $4M. No IL inheritance tax. Ownwell manages the appeal with no upfront cost.
Courts & Legal
Courts & Legal
Circuit Court (Probate): The St. Clair County Circuit Court – 20th Judicial Circuit at 10 Public Square, Belleville, IL 62220, phone 618-277-7325, handles probate, estate administration, and all civil and criminal matters.
Recorder of Deeds: The St. Clair County Recorder at 10 Public Square maintains real property records. Land records searchable online.
Senior Services
The St. Clair County Illinois Department on Aging and the Area Agency on Aging Southwestern Illinois serve the county’s senior population. Contact the county’s Human Services Department at 10 Public Square, Belleville. HSHS St. Elizabeth’s Hospital and Memorial Hospital provide significant geriatric care.
Recommended
Assisted living, memory care, and independent living across St. Clair County - from Belleville and O'Fallon to Fairview Heights, Swansea, and the Mississippi River communities.
Marriage & Vital Records
Marriage licenses, divorce records, and birth & death certificates are handled by the following office(s):
COUNTY CLERK (Records, Vital Records, Elections)
10 Public Square, Belleville, IL 62220
(618) 277-6600
CIRCUIT CLERK (Court Records, Marriage Licenses)
10 Public Square, Belleville, IL 62220
(618) 277-7325
ELECTIONS (County Clerk)
10 Public Square, Belleville, IL 62220
(618) 277-6600
Genealogy
County-level record sources
St. Clair County Circuit Clerk (probate/estate case files – see Probate section above).
As Illinois’ oldest county (1790), St. Clair holds particularly deep colonial and territorial-era records of genealogical interest.
Local societies
No dedicated St. Clair County genealogical society was confirmed in available directories.
Probate & Estate
Losing someone and having to deal with courts and paperwork at the same time is hard. This section won’t make that easier, but it should tell you what to expect, what it costs, and where to go – so at least you’re not walking in blind.
Where to go
St. Clair County Circuit Clerk 10 Public Square, Belleville, IL 62220 (618) 825-2334
St. Clair County is one of Illinois’ most populous counties, part of the Metro-East region across the Mississippi River from St. Louis, Missouri. St. Clair County is one of only 7 single-county judicial circuits in Illinois. It is Illinois’ oldest county, established in 1790 under the Northwest Territory.
Step 1: figure out which path applies
Illinois has NOT adopted the Uniform Probate Code and is not a community property state – it follows common law property principles. Illinois probate is governed by the Probate Act of 1975 (755 ILCS 5/). Two main paths:
Small Estate Affidavit – for estates where personal property (excluding real estate) is valued at $150,000 or less (raised from $100,000 effective August 15, 2025), with no unresolved debts or claims and no real estate involved. No formal court probate is required.
Formal Probate (Independent or Supervised Administration) – required when the estate doesn’t qualify for the small estate affidavit. Most Illinois probate cases proceed under Independent Administration, letting the estate representative act without prior court approval for most routine actions.
Step 2: filing for formal probate
File the decedent’s original will (if one exists) with the St. Clair County Circuit Clerk, where the decedent resided at death.
Petition the court to open the estate and appoint an executor (if there’s a will) or an administrator (if intestate).
The court issues Letters of Office (Letters Testamentary or Letters of Administration) appointing the representative.
Publish notice to creditors and unknown heirs as required by Illinois law.
Under Independent Administration, the representative marshals assets, pays valid debts and taxes, and distributes the remaining estate without needing court approval for each step.
File a final accounting or closing documents to formally close the estate.
What it costs
Illinois imposes its own state estate tax on estates valued above $4 million, with rates up to 16%. There is no Illinois inheritance tax.
Filing fees vary by county – confirm current amounts with the St. Clair County Circuit Clerk.
Most uncontested probate proceedings in Illinois can be completed within about a year.
Probate filings, estate administration, and guardianship matters are handled by the following office(s):
Public Safety & Arrests
Arrest records, inmate search, and law enforcement services are handled by the following office(s):
SHERIFF
700 N. Illinois St., Belleville, IL 62220
(618) 825-2027
Elections & Voting
Voter registration, polling locations, and elections information are handled by the following office(s):
COUNTY CLERK (Records, Vital Records, Elections)
10 Public Square, Belleville, IL 62220
(618) 277-6600
ELECTIONS (County Clerk)
10 Public Square, Belleville, IL 62220
(618) 277-6600
Health & Human Services
Offices & Contacts
Health services, social services, and assistance programs are handled by the following office(s):
St. Clair County Health Dept
(618) 825-4565
IL DCFS — Belleville
(618) 583-2100
IL Medicaid
(800) 843-6154
HSHS St. Elizabeth's Hospital (O'Fallon)
hshs.org/st-elizabeths
Memorial Hospital (Belleville)
memhospital.com
Touchette Regional Hospital (Centreville)
touchette.org
SSM Health St. Mary's Hospital (O'Fallon)
ssmhealth.com
Public Health Information
PUBLIC HEALTH
Office: St. Clair County Health Department – confirm current contact via co.st-clair.il.us.
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Recommended for Illinois
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