Quincy ( ), 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. It was once Illinois' second-largest city, surpassing
Peoria in 1870. The city holds several historic districts, including the
Downtown Quincy Historic District and the
South Side German Historic District showcasing the architecture of Quincy's many German immigrants from the late-19th century.