Mill Green Historic District  The Mill Green Historic District is a National Register of Historic Places listed community located in Street, Maryland. The district consists of a small cluster of privately owned historic homes and buildings including a historic mill. The district is located at the junction of Mill Green Road and Prospect Road. Broad Creek flows through the district. At some point earlier in history, the district was the home of the area post office before the post office was moved to Street, Maryland. The historic district designation was established in 1993.