area of land, eastern Wisconsin, U.S. Lying between Green Bay and Lake Michigan (Michigan, Lake), Door Peninsula is about 80 miles (130 km) long and 25 miles (40 km) wide at its base and tapering northeastward. It is crossed southeast-northwest by a waterway at Sturgeon Bay. The peninsula includes Door county (formed 1851), comprising the northern area, and parts of Kewaunee (1852) and Brown (1818) counties at the base. Communities on the peninsula include Egg Harbor, Ellison Bay, Jacksonport, Baileys Harbor (oldest village in Door county, founded 1849), Ephraim, Fish Creek, Sister Bay, Sturgeon Bay, Algoma, Kewaunee, and Washington (on Washington Island, off the tip of the peninsula).

Door Peninsula, which was visited in the 17th century by French traders and missionaries, is now a popular year-round vacation area. It is known for its fish boils, where whitefish, potatoes, and onions are cooked together in a pot over an open fire. Cherry growing, dairy farming, and tourism are also economically important. At its tip between Washington Island and the main peninsula is a hazardous strait known as Porte des Morts (French: “Death's Door”), from which the county's and the peninsula's name derives.