Decatur is a city in the U.S. state of Alabama. It is the county seat of Morgan County. The population was 57,938 at the 2020 census. Decatur is located on the banks of the Tennessee River, about 120 miles north of Birmingham. The city is a major industrial center, and is home to a number of manufacturing plants. Decatur is also a popular tourist destination, and is home to a number of historical sites, including the Decatur Museum, the First Presbyterian Church, and the Old State Bank of Alabama.