William O. Butler House was created in 1819.
William O. Munsell House was created in 1902.
William O. Douglas Wilderness was created in 1984.
William O. Douglas Federal Building was created in 1912.
B. O. Cutter House was created in 1856.
O. E. Rolvaag House was created in 1912.
Reed O. Smoot House was created in 1892.
Henry O. Tanner House was created in 1872.
Horace O. Moss House was created in 1831.
Fred O. Miller House was created in 1914.
O. E. Walker House was created in 1916.
Andrew O. Anderson House was created in 1916.
Sen. Joseph O. Clark House was created in 1924.