Fulton is a city in Whiteside County, Illinois, United States. The population was 3,481 at the 2010 census, down from 3,881 in 2000. Fulton is lo…Fulton is a city in Whiteside County, Illinois, United States. The population was 3,481 at the 2010 census, down from 3,881 in 2000. Fulton is located across the Mississippi River from Clinton, Iowa. A post office called Fulton has been in operation since 1838. The city was named for Robert Fulton, inventor of the steamboat.