[2] The District is divided into three major sections: the traditional downtown of Mount Carroll, including the courthouse, library and business district; a residential area to the south of the downtown; and further south, the historic original campus of Chicago's Shimer College, now occupied by the Campbell Center for Historic Preservation Studies.

The District's boundaries include a total of 272 buildings and structures, of which 81 have been assessed to have particular architectural and historic significance.

Two buildings that formed part of the Shimer College campus, but were built after 1960, are omitted from the Historic District: these are the Karyn Kupcinet Playhouse and the New Men's Dorm, both of which are separated from the rest of the campus by Jackson Street.

Since Shimer's departure in 1978, the campus has been occupied by the Campbell Center for Historic Preservation Studies, originally known as the "Restoration College".

The buildings are used for administrative, classroom, and lodging purposes, but also serve as subject matter for the study and practice of historic preservation.