Ottawa is a city in, and the county seat of, Franklin County, Kansas, United States. It is located on both banks of the Marais des Cygnes River ne…Ottawa is a city in, and the county seat of, Franklin County, Kansas, United States. It is located on both banks of the Marais des Cygnes River near the center of Franklin County. As of the 2020 census, the population of the city was 12,625. It is the home of Ottawa University.