Chelsea is a city in Shelby County, Alabama, United States. Chelsea was incorporated on March 1, 1996 with a population of 906. At the 2000 census the population was 2,949. According to U.S. Census Bureau, the 2008 population estimate for Chelsea was 4,303. Chelsea is widely considered the fastest growing city in Shelby County, which is the fastest growing county in the state of Alabama.