In 1876 Lafaytte French, a buffalo hunter and Indian trader from Pennsylvania, USA, met Orville Hawkins Smith, a mule skinner who drove teams between Salt Lake City and Montana, and the seeds of the OH Ranch were planted. In 1878 the two frontiersmen established an Indian trading post at Blackfoot Crossing, only to have it closed by the North West Mounted Police a year later because of the usurious prices charged. Non plussed by the event, the two men moved to what is now High River, Alberta and opened the soon-to-be town's first legitimate business, a stopping house for settlers traveling to their new homesteads.

In 1881, the two raconteurs bought some cattle and began squatting at what is now the Main Headquarters of the OH Ranch. The two men decided to use Smithy's initials to brand their cattle. The OH brand was the twenty-fifth cattle brand registered in what was then known as the North West Territories. Perhaps unknown to the two fledgling ranchers, the letters O and H are two of only seven characters which cannot be branded upside down or backwards.

In 1883 Smith and French sold the brand and their cattle to Frederick Ings, who had moved west from his native Prince Edward Island. This marked the official recognition of the ranch. The following year Walter Ings joined his brother's new cattle venture and the operation was named Rio Alto Ranch, which means High River in Spanish.

In 1890, with the ranch firmly established on the banks of the Highwood River, Canadian Senator Dan Riley and Phil Weinard constructed a North West Mounted Police Post cabin near the main headquarters of the ranch. While the original building was destroyed by fire in 1962, it was re-created by Doc Seaman in its original form in 1989 near the cookhouse at the Main Headquarters of the OH Ranch.

In 1900 the OH brand was officially transferred to Walter Ings, who continued to operate the ranch. The winter of 1906-07 had drastic impacts on ranching in the High River district with nearly 75% of the cattle in the area killed by the harsh winter. In 1907, the last general round-up of cattle in the area was held and fences began to appear on the open ranges of the Eastern Slopes of the Canadian Rocky Mountains.

In 1918, Walter Ings sold the ranch, its cattle and the OH brand to Pat Burns, one of the "Big Four" who had started the Calgary Exhibition and Stampede a few years earlier. Burns soon sold the operation to Mayer and Lage Steamship Company. This corporation had a large beef contract with Belgium and this ownership continued for the next 20 years, until Burns regained control of the ranch and brand in 1938.

In 1950, the ranch was sold again, this time to Kirk Roenisch and Bill Arden.It was at this time that the name of the ranch was officially changed from Rio Alto to OH Ranch Ltd. Later the ranch was sold to A.D. "Doug" Kingsford, Arden's son-in-law. Bert Sheppard, then the manager and part owner of the ranch, ensured the continuation of the Rio Alto name by erecting a sculptured metal sign on the front gates tot he ranch's main entrance. This sign continues to greet visitors today.

In 1987 D.K. 'Doc' Seaman purchased the 18,000 acre ranch as well as the OH brand and the entire herd of commercial Hereford cattle. Many see Mr. Seaman as the savior of the ranch as the Canadian Military had been making arrangements to purchase the OH and turn it into a training ground for Canadian and NATO troops. The following year, in 1988, Bud Maynard joined the operation as Ranch Manager, bringing his wife Brenda and their children Melissa and TJ. In 1988 the OH began to formalize and implement the Range Tested Program.

Since then, Doc Seaman has continued to develop and expand the scope of the ranch's operations. In 1991 a 9,700 acre ranch was purchased near Bassano, Alberta to serve as a base for the breeding of the OH Ranch's Range Tested® Red Baldy Heifers, raised for the Annual Production Sale in November and as replacements for Longview and Dorothy. In 1993 the operation was expanded again with the purchase of a 20,050 acre ranch near Dorothy, Alberta. The OH also purchased the renowned Elkink herd of Line-One Herefords which had been ranged in the Saskatchewan Sand Hills for the previous 50 years. This remarkable set of cattle had all the right characteristics to join the OH Range Tested® Program and were soon installed at the Dorothy operation. In 1994, another 4,300 acres, the heart of the historic Bar U Ranch winter range, was incorporated into the OH operation with the purchase of the Pekisko property and Winter Range Inc. This ranch, located a few miles south of the OH Ranch's main headquarters, has become the home of the OH Ranch's bull herds as well as augmenting the winter pasture of the Longview ranch.

With the purchase of the OH ranch in 1987, Doc Seaman began a vigorous program of upgrading the ranch as well as maintaining and preserving the history of the operation. Visitors to the OH operation at Longview can view a replica of the original North West Mounted Police Post as well as tour the cook-house, which was originally constructed by the Ings brothers in the 1800's.

Since its inception in 1883, the OH Ranch has always operated using traditional methods. Today, cowboys continue to ride the range, moving cattle and doctoring sick animals in the open field by roping from horseback. While the ranch owns trucks and other equipment, horses are still the primary mode of transporation on the ranch and continue to be used for such tasks as packing fencing supplies, minerals and salt and protein blocks. The OH Ranch is one of the few large cattle outfits in North America which continues to be operated utilizing historic methods.