Monroe County is a county located in the U.S. state of Illinois. According to the 2020 census, it had a population of 34,962. Its county seat and largest city is Waterloo.
Monroe County Courthouse in Waterloo
J. B. Bridge during the flood of 1993
Waterloo is a city in and county seat of Monroe County, Illinois, United States. The population was 11,013 at the 2020 census, up from 9,811 in 2010.
Monroe County Courthouse in the Waterloo Historic District
View over Porta Westfalica, Germany, Waterloo's sister city
Fountain Creek Bridge, west of the city limits