Waterloo Flag

Waterloo

County:
Monroe County
County Seat:
Yes
Area (mi²):
8.234
State:
Illinois

Waterloo is a city located in Monroe County, Illinois. Waterloo has a 2026 population of 11,165. It is also the county seat of Monroe County. Waterloo is currently declining at a rate of -0.33% annually but its population has increased by 1.46% since the most recent census, which recorded a population of 11,004 in 2020.

11.2K
Total Population
1,356
Density (mi²)
-37 -0.33%
Growth

Nearby Cities

Sources

  1. US Census State Population Estimates - Most recent state estimates from the Census Bureau's Population Estimates Program
  2. US Census County Population Estimates - Most recent county estimates from the Census Bureau's Population Estimates Program
  3. American Community Survey (2009 - 2013)
  4. Census QuickFacts
  5. Historical Populations of States and Counties (1790 - 1990)