Spencer is a city in the state of Iowa (United States), and the county seat of Clay County. It is located at the confluence of the Little Sioux and Ocheyedan rivers. The population was 11,233 in the 2010 census, a decline from 11,317 in the 2000 census. Spencer has a notable Clay County Fair, held annually in September, which averages more than 300,000 visitors each year.
The town's late library cat, Dewey Readmore Books, became known throughout the world before his death in 2006. He was immortalized in the book Dewey: The Small-Town Library Cat Who Touched the World by Vicki Myron, director of the library, and Bret Witter.