Ottawa is a city located in LaSalle County, Illinois, in the United States. It serves as the county seat and functions as the principal city of the Ottawa, Illinois, micropolitan area. According to the 2020 census, the city had a population of 18,840.
The city is situated at the confluence of the navigable Fox River and the Illinois River. The Illinois River serves as a significant transportation route for river barges, connecting Lake Michigan at Chicago to the Mississippi River.