Quincy (/ˈkwɪnsi/ KWIN-see), known as Illinois's "Gem City," is a city on the Mississippi River and the county seat of Adams County, Illinois, United States. As of the 2010 census the city held a population of 40,633, up from 40,366 in 2000. During the 19th Century, Quincy was a thriving transportation center as riverboats and rail service linked the city to many destinations west and along the river.