The Parish House adjacent to the church at 1525 H Street, N.W. was built in 1836. It is a National Historic Landmark. It was the residence in 1842 of Alexander Baring, Lord Ashburton, who negotiated a treaty that year with U.S. Secretary of State Daniel Webster. This treaty established the final boundaries between Canada and the United States from Maine to Minnesota, and helped avert a possible war between Great Britain and the United States. The building, also known as Ashburton House, later served for a period, prior to the Civil War, as the site of the British Legation to the U.S.