 A return to politics was planned for 1910, when Sibley was nominated once again for Congress, running for what would have been his sixth term in Washington.His plan was short-circuited by a severe heart attack in that year, however, leaving Sibley unable to campaign and he was forced to resign the nomination, thereby effectively ending his political career.During his later years, Sibley resumed his former manufacturing and agricultural pursuits at his well-known estate, "River Ridge Farm," located near Franklin, Pennsylvania.