The Door Peninsula is a peninsula in eastern Wisconsin, separating the southern part of the Green Bay from Lake Michigan. The peninsula includes northern Kewaunee County, northeastern Brown County, and the mainland portion of Door County. It is on the western side of the Niagara Escarpment. Well known for its cherry and apple orchards, the Door …The Door Peninsula is a peninsula in eastern Wisconsin, separating the southern part of the Green Bay from Lake Michigan. The peninsula includes northern Kewaunee County, northeastern Brown County, and the mainland portion of Door County. It is on the western side of the Niagara Escarpment. Well known for its cherry and apple orchards, the Door Peninsula is a popular tourism destination. With the 1881 completion of the Sturgeon Bay Ship Canal, the northern half of the peninsula became an island.