The Katharine Seymour Day House is a historic house at 77 Forest Street in the historic Nook Farm district of Hartford, Connecticut. Built in 1884 for a local businessman seeking to compete stylistically with the adjacent Mark Twain House, it is a good local example of Queen Anne architecture. It now serves as the administrative center and library for the Harriet Beecher Stowe Center. It was listed on the National Register of Historic Places in 1971.