what county is ottawa il
Ottawa, IL. Sponsored Topics. Ottawa is a city located at the confluence of the Illinois River and Fox River in LaSalle County, Illinois, USA. As of the 2000 census, the city population was 18,307. It is the county seat of LaSalle County and it is part of the Ottawa-Streator Micropolitan Statistical Area, which was the 259th-most populous area in the United States in 2007.