The black-crowned night heron is 23-28 inches tall. It has a wingspan of almost four feet. It is a medium-sized heron with a stocky body and short legs and neck. It has a black crown and back, grey wings and a white underside.

Adults have red eyes and yellow legs and feet. In breeding season adults have two long white plumes on their heads. Females and males look alike, but females are a little smaller. Immature night herons have a grey-brown head, chest and belly streaked with white. Their eyes are yellow and they have grey legs. Black-crowned night herons don't have adult plumage until they are about three years old.