The General John Frelinghuysen House was the homestead of the Frelinghuysen family, significant in New Jersey history. General John Frelinghuysen was an attorney who served as a Brigadier General during the War of 1812 and was later the Surrogate of Somerset County. The main part of the house was originally constructed as a one-and-a-half story brick structure in 1750, and it was General Frelinghuysen who added the second floor to the brick section in the early 19th century. The Greek Revival porch, with four Doric columns, was added in the mid-19th century. The interior of the house, now the Raritan Public Library, is finished with a graceful stairway.