Illinois · FIPS 17123 · County seat: Lacon
Marshall County, IL GIS & Parcel Viewer
Parcel lookups for Marshall County start at the Marshall County myGISonline viewer. This page gives you that official link, notes on how the viewer works, and links to the counties next door.
Open the Marshall County parcel map ↗
Opens portico.mygisonline.com in a new tab. We link out and never embed or copy parcel data.
Quick facts
| Official map | Marshall County myGISonline viewer |
|---|---|
| Type | County-run map |
| Website | portico.mygisonline.com |
| Access | Free, no login (checked Oct 2026) |
| County seat | Lacon |
| Population | 11,683 (2023 Census Bureau estimate) |
| Land area | 387 sq mi |
| FIPS code | 17123 |
Where the parcel data comes from
Marshall County runs this viewer (directly or through a contracted vendor), which makes it the closest thing to the source for local parcel lines. As of our October 2026 test, anyone could open it without signing in or paying.
Finding a property on this map
- Press the button above. This county's viewer runs on myGISonline; 13 counties in our directory use the same service.
- Find the search option and look up a property, or zoom in on the map.
- Click a lot to see its details.
- Check the toolbar for layers, measuring and printing.
Many parcel sites expect owner names last name first. If a full name finds nothing, try just the surname.
About Marshall County
The U.S. Census Bureau estimated Marshall County's population at 11,683 in 2023, spread over about 387 square miles of land, or roughly 30 people per square mile. That makes it number 84 out of 102 Illinois counties by population. Lacon serves as the county seat.
Nearby parcel maps
Marshall County shares a border with the counties below. Each link has its own official map:
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.