The Thankful Arnold House, on Hayden Hill Road in Haddam, was built in three stages between 1794 and 1810. The first section, built in 1794-1795 by Linus Parmalee, was a small house, with a shop on the first floor. The mortgaged house was foreclosed in 1797 and sold to Joseph Arnold, a merchant who had his shop in the basement. In 1800, the second section was built adding two bays to the western end of the house. The third section to be added, in 1810, was an extension to the rear, making the gambrel-roofed house have a saltbox profile. The two-story ell on the west side, which was originally a separate mid-eighteenth century building, was also added at this time. Joseph Arnold died in 1823 and his widow, Thankful Clark Arnold, continued to live in the house, which was known as the Widow Arnold House, until her death in 1849. It was occupied by Arnold descendants until it was purchased in 1963 by one who lived in Texas, Isaac Arnold, who died in 1973, leaving the house to the Haddam Historical Society. By that time, the house had already been restored to its 1810 appearance and opened to the public as a museum in 1965.