Highway 804 is 21.4 kilometres (13.3 mi) long, and connects Highway 105 south of the town of Ear Falls with the hydroelectricdam at Lower Manitou Falls. The short highway travels entirely through an uninhabited forested region dotted with lakes and swamps. Near the western end of the route, a logging road branches northwest that provides a rough and winding connection to Highway 658 as well as to the northern terminus of Highway 105 in Red Lake.
On an average day, only 70 vehicles travel along the highway.
Highway 804 was designated on April 25, 1962. It was paved in 1969. At that time, it was the only tertiary highway in Ontario that was paved, but it has since reverted to a loose gravel surface highway. The route and length of the highway have remained unchanged since it was designated.