The Old Grafton County Courthouse is a historic courthouse building at 1 Court Street in Plymouth, New Hampshire. This modest wood frame building was built in 1774 to serve as one of two courthouses for Grafton County, which had just been established; it is one of the oldest surviving civic structures in the state. It was described at the time of its construction as having \"a stately cupola out of proportion to the diminutive size of the structure\". After a new courthouse was built in 1823, the building was sold and moved to the outskirts of Plymouth, and used as a wheelwright's shop, undergoing significant alteration to accommodate that function. In 1876 the building was acquired by the Young Ladies' Library Association, which moved it to its present location and restored it. It is now the museum of the Plymouth Historical Society.
The building was listed on the National Register of Historic Places in 1982, and included in the Plymouth Historic District in 1986.
