Freshwater marshes and brackish tidal marshes. The king rail is the largest North American rail, with an appearance similar to that of the more common clapper rail, whose habitat is generally restricted to saltwater marshes. The slightly larger king rail has a more brownish appearance than the grayish clapper rail. Also, the barring on the flanks of the king rail shows greater definition, and the king rail has a more red-brown breast.
Sexes are similar, but the male is slightly larger.
The king rail nests locally in freshwater wetland habitats from the Atlantic coast west to the Great Plains. Southern New England is the northern extreme of its eastern range. The species winters along the coast from Connecticut south to the Gulf of Mexico. King rails are known to return to the same nesting area year after year. The nest is in a grass-lined depression on the ground or slightly elevated in the branches of wetland shrubs such as buttonbush.