LaSalle County, Illinois

County seat: Ottawa · Population 107,773 (2025) · 1,135 sq mi

LaSalle County is the 17th most populous of Illinois's 102 counties, with 107,773 people (2025 estimate). Its county seat is Ottawa. It is part of the Northwest region, one of the 10 Illinois economic development regions (DCEO). The map shows its 27 cities and towns and the 9 neighboring counties.

Map of LaSalle County, Illinois with cities, towns and the county boundary
LaSalle County, Illinois with its cities and towns, unincorporated communities (CDPs) and neighboring counties. Boundaries: U.S. Census Bureau, 2025. Free to use with attribution (CC BY 4.0).
Download PDF (Letter) 139 KBPNG image 100 KBIllinois county map

LaSalle County facts

County seat
Ottawa
Population (2025 estimate)
107,773 −1.7% since 2020
Land area
1,135 sq mi 2nd largest of 102
Water area
13 sq mi
Population density
95 per sq mi
Established
1831
Named after
René-Robert Cavelier, Sieur de La Salle 17th-century French explorer and fur trader in North America
Largest city
Ottawa 18,684
Median household income
$73,045
Cities and towns
27 plus 6 CDPs
ZIP codes
29
Time zone
Central
FIPS code
17099

Cities and towns in LaSalle County

LaSalle County has 27 incorporated cities, towns and villages. Populations count the people living inside LaSalle County; cities that cross a county line also list the other counties.

NameTypePopulation 2025Also in
Ottawa (county seat)City18,684
StreatorCity12,127Livingston County
PeruCity9,777Bureau County
LaSalleCity9,388
MendotaCity6,894
MarseillesCity4,809
OglesbyCity3,618
SenecaVillage2,302Grundy County
SheridanVillage2,094
EarlvilleCity1,590
North UticaVillage1,334
LelandVillage928
TonicaVillage737
Grand RidgeVillage508
LostantVillage428
MillingtonVillage420Kendall County
NaplateVillage414
RansomVillage309
Cedar PointVillage259
RutlandVillage254
SomonaukVillage231DeKalb County
KangleyVillage225
Troy GroveVillage225
DanaVillage162
LeonoreVillage119
WenonaCity15Marshall County
DalzellVillage0Bureau County

Unincorporated communities (CDPs)

Census-designated places are communities without their own city government; the county provides their services.

CommunityPopulationAlso in
Lake Holiday5,641
Dayton271
Serena182
Triumph83
Harding18
Wedron0

ZIP codes in LaSalle County

29 ZIP codes reach into LaSalle County. ZIP codes ignore county lines, so some also cover a neighboring county.

Population of LaSalle County, 2020–2025

LaSalle County shrank by 1,872 people (−1.7%) between April 2020 and July 2025: 1,662 more deaths than births and a net loss of 209 people from migration.

Year (July 1)Population
2020109,411
2021108,679
2022107,798
2023107,872
2024107,875
2025107,773

Neighboring counties

Printable LaSalle County map

The PDF is a vector file with real text: it prints sharp on Letter paper and you can search it for a town. The PNG is 2400 pixels wide for slides and documents. Both are free to use with a credit to WhichCounty.

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Sources

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