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County · code 29099

Jefferson CountyMissouri

Jefferson County is in Missouri with its county seat in Hillsboro. It was created in 1819 from parts of St. Louis and Ste. Genevieve counties and named after Thomas Jefferson.

  • Founded1819
  • County seatHillsboro
  • Named forThomas Jefferson
  • Land area656 sq mi + 7.8 sq mi water
  • Population226,739 2020 Census
  • Parcels mapped106,538 checked 15 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

Monroe, ILSt. LouisWashingtonSt. FrancoisSte. GenevieveFranklin Hillsboro Census outline · seat marked

Where it is

Jefferson on the map of Missouri

Missouri has 115 counties and county equivalents, each with its own records office. Shapes with a page are links.

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Counties of Missouri · Jefferson highlighted

History

Formed in 1819 from St. Louis County and Ste. Genevieve County

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

Jefferson County was created in 1819 from St. Louis and Ste. Genevieve. In 1821 the county lost territory to the creation of St. Francois County, and in 1825 it gained from Ste. Genevieve but lost to Washington.

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

  1. 1819
    Jefferson County created Jefferson created from St. Louis and Ste. Genevieve.
    from St. Louisfrom Ste. Genevieve
    · Mo. Terr. Laws 1818-1819, ch. 220, secs. 1, 10/pp. 554-558
  2. 1821
    Lost territory Jefferson lost to creation of St. Francois.
    to St. Francois
    · Mo. Laws 1821-1822, ch. 26, sec. 1/pp. 28-30
  3. 1825
    Gained territory Jefferson gained from Ste. Genevieve, lost to Washington.
    from Ste. Genevievefrom Washington
    · Mo. Laws Rev., 1825, ch.1, sec. 8/p. 234
  4. 1831
    Boundary clarified Boundary between Jefferson and Ste. Genevieve clarified (no change).
    with Ste. Genevieveno change
    · Mo. Laws 1830-1831, pub., ch. 17, sec. 3/pp. 24-25 and Mo. Laws 1832-1833, pub., ch. 34, sec. 2/p. 57
  5. 1849
    Lost territory Jefferson lost to Ste. Genevieve.
    to Ste. Genevieve
    · Mo. Laws 1848-1849, pub., pp. 32-33
  6. 1859
    Changed Boundary between Jefferson and Ste. Genevieve defined (no change).
    Ste. Genevieve
    · Mo. Laws 1858-1859, p. 361
  7. 1870
    Changed Jefferson's and Ste. Genevieve's boundaries defined (no change).
    Ste. Genevieve
    · Mo. Laws 1870, adj. sess., gen., pp. 32-33

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
226,739 2020 Census count
Housing units
92,385 2020 Census count
Land area
656 square miles
Water area
7.8 square miles
People per sq mi
345 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.

Permits

County government

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 St. Louis County and Ste. Genevieve County, and named after Thomas Jefferson.
What is the county seat of Jefferson County?
The county seat of Jefferson County is Hillsboro.
Is there an online parcel map for Jefferson County?
Yes. A public source publishes a parcel map of 106,538 parcels, rated good enough 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 St. Louis County and Ste. Genevieve County. Since then the Atlas of Historical County Boundaries records 3 later changes, chiefly involving Ste. Genevieve County, St. Francois County and Washington County.
Who issues building permits in Jefferson County?
The county's page on building permits: Permits & Licenses. Inside a city or town, ask that city first.
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