The first courthouse was located in Melbourne. A portion of this building was also used for a grocery store.
The county seat was relocated to LaMars in 1872 when its citizens offered to provide a suitable courthouse for county use. This building served the county until 1874, when a new $3,000 building was constructed.
The county's population grew and so another courthouse was needed. This building, which serves as the present courthouse, was completed in 1902. Today its red sandstone exterior remains nearly as it was when first built, except that a large cupola was removed. Plymouth has plans for a new courthouse to be completed in 1998.