- Decatur is a city in the state of Alabama, located in Morgan and Limestone counties. It is situated along the Tennessee River and is part of the Huntsville-Decatur Combined Statistical Area. Decatur has a population of approximately 55,000 people and covers an area of 58.5 square miles. The city is known for its historical sites, outdoor recreational opportunities, and vibrant downtown area. Notable attractions in Decatur include the Old State Bank, Point Mallard Park, and the Cook's Natural Science Museum. The city also has a strong industrial presence, with several major manufacturing plants and industries situated in the area.