Illinois · FIPS 17081 · County seat: Mount Vernon
Jefferson County, IL GIS & Parcel Viewer
Parcel lookups for Jefferson County start at Jefferson County Assessor Portico map. This page gives you that official link, notes on how the viewer works, and links to the counties next door.
Open the Jefferson County parcel map ↗
Opens portico.sidwellco.com in a new tab. We link out and never embed or copy parcel data.
Jefferson County at a glance
| Official map | Jefferson County Assessor Portico map |
|---|---|
| Type | County-run map |
| Website | portico.sidwellco.com |
| Access | Free, no login (checked Oct 2026) |
| County seat | Mount Vernon |
| Population | 36,320 (2023 Census Bureau estimate) |
| Land area | 571 sq mi |
| FIPS code | 17081 |
About the official source
It is a county-level map: Jefferson County or the company it hires keeps the parcel layer up to date. When we tested the link in October 2026 it opened with no login and no fee.
How to use the Jefferson County viewer
- Open the official link; the viewer runs on Esri's ArcGIS platform.
- Find the search control and type in a street address or parcel ID, or zoom in by hand.
- Click a parcel to see the attributes the publisher shares.
- Use any layer or basemap tools to add aerial imagery or other map layers.
If an address search comes up empty, try the parcel number from a tax bill or deed instead, or click the lot on the map.
The county in brief
Census Bureau figures put Jefferson County at about 36,320 people (2023 estimate) on roughly 571 square miles of land, which is about 64 residents per square mile. That makes it number 38 out of 102 Illinois counties by population. Mount Vernon serves as the county seat.
Nearby parcel maps
Parcels close to the edge of Jefferson County can fall in the next county over. Neighboring counties:
Maps vs. surveys
Online parcel lines are drawn for tax and planning use. They can be off by several feet, so use a recorded plat or a licensed surveyor for fences, setbacks or a sale.