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County · code 17081

Jefferson CountyIllinois

Jefferson County is in Illinois with its county seat in Mount Vernon. The county was formed on March 26, 1819.

  • Founded1819
  • County seatMount Vernon
  • Named forThomas Jefferson
  • Land area571 sq mi + 13 sq mi water
  • Population37,113 2020 Census
  • Parcels mapped30,892 checked 14 October 2026
Open the free map Click any parcel in Jefferson County: acreage, parcel id, address and who publishes the map. No sign-in.

Updated

FranklinMarionPerryWayne Mount Vernon Census outline · seat marked

Where it is

Jefferson 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 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 CountySt. Clair CountySaline CountySangamon CountySchuyler CountyScott CountyShelby CountyStark CountyStephenson CountyTazewell CountyUnion CountyVermilion CountyWabash CountyWarren CountyWashington CountyWayne CountyWhite CountyWhiteside CountyWill CountyWilliamson CountyWinnebago CountyWoodford CountyJefferson County Jefferson
Counties of Illinois · Jefferson highlighted

History

Formed in 1819 from Edwards County and White County

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

Jefferson County was created from Edwards and White counties. The county was named after Thomas Jefferson. In its early years, Jefferson County lost territory to the creation of Fayette County in 1821 and Marion County in 1823.

Boundary changes from the Newberry Library, Atlas of Historical County Boundaries.

  1. 1819
    Jefferson County created Jefferson created from Edwards and White.
    from Edwardsfrom White
    · Ill. Laws 1819, pp. 267-268
  2. 1819
    Gained territory Jefferson gained from Edwards.
    from Edwards
    · Ill. Laws 1819, pp. 320-321
  3. 1821
    Lost territory Jefferson lost to creation of Fayette.
    to Fayette
    · Ill. Laws 1820-1821, pp. 164-167
  4. 1823
    Lost territory Jefferson lost to creation of Marion.
    to Marion
    · Ill. Laws 1822-1823, pp. 49-50

Land and parcels

What the maps cover in Jefferson

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

Jefferson by the Census

Population
37,113 2020 Census count
Housing units
16,632 2020 Census count
Land area
571 square miles
Water area
13 square miles
People per sq mi
65 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

Zoning and code

GIS and maps

County government

  • County government

    The official website of Jefferson County.

    jeffersoncounty.illinois.gov

See your own lot on these maps

Open Jefferson 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 Jefferson County

When was Jefferson County founded?
Jefferson County was founded in 1819, formed from Edwards County and White County, and named after Thomas Jefferson.
What is the county seat of Jefferson County?
The county seat of Jefferson County is Mount Vernon.
Is there an online parcel map for Jefferson County?
Yes. Jefferson County publishes a parcel map of 30,892 parcels, rated official here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.
Has Jefferson County's boundary or name changed?
Jefferson County was created in 1819 from Edwards County and White County. Since then the Atlas of Historical County Boundaries records 3 later changes, chiefly involving Edwards County, Fayette County and Marion County.
Is my lot in a flood zone?
We do not have flood maps for Jefferson 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