Nerodia erythrogaster, commonly known as the plain-bellied watersnake, is native to the southeastern United States. Its geographical distribution spans from southeastern Kansas and Missouri, eastward through Kentucky and Tennessee, and extends south through most of Mississippi, Alabama, and Georgia into Florida. It is also found as far west as eastern Texas and eastern Oklahoma.

Nerodia erythrogaster primarily inhabits freshwater environments. It is typically found in habitats such as ponds, lakes, rivers, streams, and swamps. These areas usually have abundant vegetation and are in regions with a temperate climate, characterized by warm to hot summers and cool winters.

The plain-bellied watersnake plays a role as both predator and prey within its ecosystem. It preys on amphibians, fish, and small mammals, making it an important part of the aquatic food web. Its typical adaptation to aquatic environments includes defensive behaviors suited to both terrestrial and aquatic predators.