Katharine Seymour Day (May 8, 1870 - June 4, 1964) was an American preservationist from Hartford, Connecticut. She worked as a member of the Hartford City Planning Commission to preserve historic homes in Connecticut and helped establish the Children’s Museum of Hartford and the home of Mark Twain as a memorial. She served as president of the Mark Twain Library and Memorial Commission.[1] She was inducted into the Connecticut Women's Hall of Fame in 1994. The Katharine Seymour Day House has been preserved as part of the Harriet Beecher Stowe House Museum.