Located just west of Colimbia, Clarksville is an unincorporated community that was settled in the 18th century by primarily immigrant farmers, including tobacco farmers. It was named for Irish immigrant James. R. Clark who purchased land here in 1790. A post office was opened in 1851; portal records from the 1930s show there were then 65 residents. Many apple orchards were found here in the early to mid 1900s. About ten miles of today's Route 108 was, in the 1890s, a private toll road connecting Ellicott City and Clarksville.