Settlers began arriving in the area in the 1870s, and a post office was established in 1888, after the name of Sidney was decided upon. The following year, Montana officially became a state. Sidney was incorporated in 1911, according to the http://www.sidneymt.com/history.htm Sidney Chamber of Commerce. The town was originally part of Dawson County, Montana, but became county seat of Richland County at its inception in 1914. Agriculture became an important part of the region after the http://www.esidney.com/sugardays/lyipsmmry.html Lower Yellowstone Irrigation Project was completed in 1909. A dam was built on the river south of Glendive, MontanaGlendive, which diverted water from the river into a 115.2 km (72 mi) main canal, which runs north-south, parallel to the Yellowstone, irrigating land from Glendive north up to Fairview, MontanaFairview, where it dumps into the Missouri River. This project irrigates 51,429 acres and serves water to 450 farms, according to the manager of the http://resourcescommittee.house.gov/archives/106cong/water/99oct07/nypen.htm Lower Yellowstone Irrigation Districts. The area experienced an oil boom and bust in the late 1970s and 1980s, bringing an influx of people to the town for a short period of time. At the turn of the century, the town started experiencing another surge in oil exploration activity. Source: http://en.wikipedia.org/wiki/Sidney%2C_Montana