Upon completion of the Milwaukee Railroad in 1910, Ingomar became the hub of commerce in an area bounded by the Missouri River to the north, the Musselshell River to the west, and the Yellowstone River to the south and east. Ingomar was an ideal location for a railhead and shipping center for the thousands of acres between the Yellowstone and the Missouri Rivers.
The townsite was platted in 1910 by the railroad and named by railroad officials. The depot was completed in 1911.
Contributing to the growth of the area north to the Missouri and south to the Yellowstone was the Homestead Act of 1862, later amended to give settlers 320 acres of land which, if proved up in 5 years, became their own. The railroad advertised the area as "Freeland" and was responsible for bringing settlers into the area.
Ingomar was also the sheep shearing center to the migratory sheepmen using the free spring, summer, and fall grass. Ingomar became the site of the world’s largest sheep shearing and wool shipping point. Two million pounds of wool a year were shipped from Ingomar during the peak years. Shearing pens in Perth, Australia, were designed using the Ingomar pens as a model. Wool was stored in the wool warehouse located adjacent to the shearing pens and shipped out by rail through 1975 when the wool warehouse was sold to William Magelssen. Rail service was discontinued in 1980.
Since potable water could not be found at the townsite, water was supplied by the Milwaukee Railroad using a water tender. The water tender was left in Ingomar as a gift by the Milwaukee Railroad when services were discontinued. In late 1984, a water system was installed for the few remaining Ingomar residents.
Between 1911 and 1917, there was an average of 2,500 homestead filings per year in this area. The post office was established in 1910, with Si Sigman as the postmaster. Ingomar soon became a bustling town of 46 businesses, including a bank, 2 elevators, 2 general stores, 2 hotels (of which, one remains), 2 lumber yards, rooming houses, saloons, cafes, drug store, blacksmith shop, claims office, doctor, dentist, maternity home and various other essential services. To the northeast of the townsite is what remains of Trout Lake, a body of water impounded by the embankment of the railroad, which provided boating and swimming in summer, skating in winter, and a source of ice that was cut, harvested, and stored in 3 ice houses to provide summer refrigeration. Fires, drought, and depression have wreaked havoc on this community over the years. The dreams of homesteaders vanished as rain failed to come in quantities to assure a crop with sufficient frequency to enable them to make a living. A reluctance to abandon the town has kept it alive through the devastating fire of 1921, which destroyed a large portion of it. Some businesses rebuilt, but others moved on.
The Ingomar Hotel located at the corner of Main Street and Railway Avenue was built in 1922 and connected to an older dining room which was managed by Mrs. H. J. Broom, and by Stena Austin after Mrs. Broom’s death. The mortgagor, Emil Lura, took over ownership and management of the property, after twice foiling Stena’s efforts to torch the hotel. At that time rates were 50 cents per night and no women allowed; after World War II rates were raised to $1 per night. The building was purchased by Bill Seward in 1966 and is no longer operated as a hotel.