This town, originally a siding for the Northern Pacific Railroad, was named to honor the homesteaders that the town owed its beginning to. When the railroad arrived at Glendive, so did hundreds of settlers and homesteaders spreading out along the Yellowstone Valley.
Near Lone Tree Creek, the current site of Sidney, homesteads began to dot the countryside. When the telegraph line connecting Fort Keogh to Fort Buford crossed the townsite in 1878, this remote part of the nation was connected with the rest of the world. Soon after, the townspeople, tired of making the trip to Newlon 10.5 miles away to post their mail, petitioned for a post office under the name Eureka. Imagine their disappointment when Washington D.C. officials informed them that the name had already been taken by another community in northwestern Montana.
The man responsible for submitting the petition, Judge H. L. Otis, employed a family named Walters. The judge, a longtime bachelor, was fond of their six-year-old son Sidney. Sidney was his constant companion and steadfast fishing buddy. When Judge Otis suggested the name of his young friend for the new post office, not an objection was heard. The community on the banks of the Lone Tree had a name. Today it is nicknamed the "Sunrise City" and is the largest town in northeast Montana.
At one time, one of the largest herds of buffalo on the North American continent roamed the area between the Yellowstone and Missouri Rivers over the land that is now present-day Richland County. These massive herds stretched for as far as the eye could see.