County Maps US

LaSalle County, Illinois

A county in Illinois, ranked 17 of 102 by population.

CountyFIPS 17099

Within Illinois
LaSalle County, highlighted, with the areas around it. Boundaries generalised from the 2025 Census cartographic boundary file; neighbour fills carry no data. The dot marks Ottawa, the county seat, located via the 2025 Census Gazetteer.

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Population
107,773
-1,638 (-1.5%) since 2020
Land area
1,135
square miles. A further 1.1% of the total area is water
Population density
94.9
people per square mile, computed rather than published
County seat
Ottawa
Seat of county government.
Established
1831
194 years ago
Largest city
Ottawa city
Population 18,684.

Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; Wikidata (CC0), Wikidata. Retrieved 30 August 2026.

Satellite view

Aerial imagery of LaSalle County with its boundary drawn on top. A map shows you the shape; this shows you what is inside it, and which side of the line a place falls on.

Aerial view of LaSalle County, Illinois from the USGS National Map, with its boundary outlined
Imagery: USGS National Map, USGS Imagery Only, public domain, requested from USGS by your browser when you reach this point on the page, at 528 by 800 pixels. The boundary is the 2025 Census cartographic boundary file, reprojected to Web Mercator to match the imagery. You can also open the USGS National Map viewer.

Where LaSalle County ranks

Position among the 102 counties of Illinois, and among all 3,144 US counties and county-equivalents. Computed from the figures on this page.

MeasureValueIn IllinoisNationally
Population107,77317th of 102586th of 3,144
Land area1,135 sq mi2nd of 102550th of 3,144
Population density94.9 per sq mi23rd of 102955th of 3,144
Median household income$73,04532nd of 102969th of 3,143

Full data for LaSalle County

Every figure below is attributed to the Census Bureau product it came from, with the vintage of that product.
MeasureValueSource and vintage
Population107,773Vintage 2025 Population Estimates
Population in 2020109,411Vintage 2025 Population Estimates
2020 estimates base?109,645Vintage 2025 Population Estimates
Land area1,135 sq mi2025 Gazetteer Files
Water area13.1 sq mi2025 Gazetteer Files
Total area1,148 sq mi2025 Gazetteer Files
Population density?94.9 per sq miComputed: Vintage 2025 estimates divided by 2025 Gazetteer land area
Median household income$73,045American Community Survey 2020-2024 5-Year Estimates
Median home value$161,900American Community Survey 2020-2024 5-Year Estimates
Median age42.2American Community Survey 2020-2024 5-Year Estimates
Households45,373American Community Survey 2020-2024 5-Year Estimates
Housing units49,843American Community Survey 2020-2024 5-Year Estimates

Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; US Census Bureau, American Community Survey, American Community Survey 2020-2024 5-Year Estimates, released 29 January 2026. Population density is computed here, not published: it divides the Vintage 2025 population estimate by the 2025 Gazetteer land area, which are two different Census products. Retrieved 30 August 2026.

How the population changed

The Census Bureau publishes the components behind an estimate, not just the total. For the year to July 2025:

Births minus deaths
-287
1,054 births, 1,341 deaths
Net migration
+178
More people moved in than moved out.

Source: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026. Retrieved 30 August 2026.

The 9 areas bordering LaSalle County

Ordered by the length of the border actually shared, which the Census Bureau publishes in its county adjacency file and which no other county reference presents.

Bordering areaStateShared borderPopulation
Livingston CountyIllinois30 mi35,057
Grundy CountyIllinois24 mi54,052
Bureau CountyIllinois19 mi32,510
Marshall CountyIllinois18 mi11,473
DeKalb CountyIllinois17 mi101,835
Lee CountyIllinois15 mi32,914
Putnam CountyIllinois14 mi5,619
Kendall CountyIllinois12 mi145,470
Woodford CountyIllinois6.1 mi38,111

Source: US Census Bureau, County Adjacency File, 2025 County Adjacency File, released 15 September 2025. Retrieved 30 August 2026.

All 102 counties of Illinois

Open the interactive Illinois county map, or jump straight to any of them.

Data on this page last rebuilt 30 August 2026. How these figures are produced.