- Oklahoma's Bennie Owen
- Oklahoma: A History
- Oklahoma: A Sense of Place
- Okmulgee
- Okoboji and the Iowa Great Lakes
- Old Abe the War Eagle
- Old Age in the New Land
- Old and New New Englanders
- Old Bill Williams: the Famous Log Rider of Colorado
- Old Boston Days & Ways
- Old Brooklyn in Early Photographs, 1865-1929
- Old Buildings of New York With Some Notes Regarding Their Origin and Occupants
- Old Cambridge
- Old Charleston Originals
- Old College Street
- Old Country Stores of New Hampshire
- Old Cowtown Museum
- Old Creole Days
- Old Cucamonga
- Old Dominion Freight Line
- Old Dominion Industrial Commonwealth
- Old Dominion University
- Old Farm
- Old Forge and the Fulton Chain of Lakes
- Old Fort
- Old Fort Snelling
- Old Forts of the Northwest
- Old Glory
- Old Heart Of Nevada
- Old Herbaceous
- Old Idaho Penitentiary
- Old Indian Legends
- Old Islam in Detroit
- Old John Brown, The Man Whose Soul is Marching On
- Old John Neptune and Other Maine Indian Shamans
- Old Jube
- Old Landmarks and Historic Personages of Boston
- Old Los Angeles and Pasadena in Vintage Postcards
- Old Mackinaw
- Old Man River
- Old Manatee
- Old Man’s Boy Grows Up
- OLD MASSA'S PEOPLE
- Old Mobile
- Old New York in Early Photographs
- Old Newsboys' Goodfellow Fund of Detroit
- Old or New School Methodism?
- Old Oraibi
- Old Orchard Beach
- Old Peninsula Days
- Old Philadelphia in Early Photographs 1839-1914
- Old Pittsburgh Days
- Old Plantation Days: Being Recollections of Southern Life Before the Civil War
- Old Plantation Days; Being Recollections of Southern Life Before the Civil War
- Old Plymouth Trails
- Old Queens, N.Y., in Early Photographs
- Old Red
- Old Riot, New Ranger
- Old Sacramento and Downtown
- Old Saybrook
- Old Saybrook
- Old Steamboat Days On The Hudson River
- Old Sylvan Beach and the Pavilions
- Old Tacoma
- Old Taverns of New York
- Old Times in the Colonies
- Old Times in the Colonies & The Story of Liberty
- Old Times in the Colonies (Illustrated Edition)
- Old Town
- Old Versailles Township
- Old Villita and La Villita Continues
- Old Washington, D.C. in Early Photographs, 1846-1932
- Old West History for Kids - Settlement of the American West (Wild West) US Western History 6th Gra...
- Old West Showdown
- Old West Swindlers
- Old West Trivia Book
- Old Yellowstone Days
- Old Yukon
- Oldest Chicago, Second Edition
- Oldest Cincinnati
- Oldest St. Louis
- Ole Mars an' Ole Miss
- Oliver Hart and the Rise of Baptist America
- Oliver P. Morton and the Politics of the Civil War and Reconstruction
- Oliver Wendell Holmes, Jr.
- Olives in California's Gold Country
- Olivia's Story
- Olmsted Falls
- Olmsted's Texas Journey
- Omaha Food
- Omaha's Historic Houses of Worship
- Omaha’s Henry Doorly Zoo & Aquarium
- Omar: A Student Historian In Training
- On a Lark
- On Becoming a Bostonian
- On Behalf of the Family Farm
- On Being Different
- On Bicycles
- On Command: An Illustrative Study Of Command And Control In The Army Of Northern Virginia, 1863
- On Corruption in America
- On Dark and Bloody Ground
- On Democracy
- On Doing Local History
- On Fly-Fishing the Northern Rockies
- On Fly-Fishing the Wind River Range
- On Gold Mountain
- On Growing Up Tough
- On Hallowed Ground
- On Her Majesty’s Secret Service
- On His Own Terms
- On Juneteenth
- On Lincoln
- On Lynchings
- On Middle Ground
- On Montauk
- On Shaky Ground
- On Shattered Ground
- On Slavery and Abolitionism
- On Soldiers and Civilians - Short Stories of the American Civil War
- On Sympathetic Grounds
- On the Banks of the Rappahannock
- On the Border With Crook
- On the Border with Crook
- On The Border With Crook
- On the Border with Crook
- On the Border with Mackenzie
- On the Carpet
- On the Constitutionality of a National Bank
- On the Courthouse Lawn
- On the Dirty Plate Trail
- On the East End
- On the Edge of the Cold War
- On the Fly: The First Years of Cincinnati Baseball 1866-1870
- On the Fringes of Power
- On The Frontlines Of Freedom
- On the Genealogy of Mortals
- On the Grid
- On the Home Front
- On the Hunt
- On the hurricane of August 1772
- On the Indian Trail - Stories of Missionary Work among Cree and Salteaux Indians
- On the Indian Trail: Stories of Missionary Work among Cree and Salteaux Indians
- On the Lam
- On the Laps of Gods
- On the Motion of the Heart and Blood in Animals
- On the Plains with General Custer
- On the Plains, and Among the Peaks: or, How Mrs. Maxwell Made Her Natural History Collection
- On the Right to Rebel against Governors
- On the Road to West Egg
- On the Run with Bonnie & Clyde
- On the Santa Fe Trail
- On the Screen
- On the Spirit of Rights
- On the Trail
- On The Trail of Delusion
- On The Trail Of Deserters
- On the Trail of Grant and Lee
- On the Trail of the Assassins
- On the Trail of the Immigrant
- On the Water
- On The Wing Of Speed
- On these Promising Shores of the Pacific
- On This Day in California History
- On This Day in Connecticut History
- On This Day in Detroit History
- On This Day in Indianapolis History
- On This Day in Kingsport History
- On This Day in Norfolk, Virginia History
- On This Day in Outer Banks History
- On This Day in South Dakota History
- On This Day in Terre Haute History
- On This Day in West Virginia Civil War History
- On This Day in Wyoming History
- On Time Delivery
- On to Chicago
- On to Oregon!
- On to the Alamo
- On Two Wings