The first Angio-Americans to settle in what is now known as Banner County were cattle ranchers in the 1860's. The area was dominated by large open-range ranches until the herd laws of 1870 and 1887 forced the big cattle companies to move farther west.
The first homestead settlement in Banner County was in 1884. Soon afterwards homesteaders flocked into the Pumpkin Creek Valley. In 1888, Banner County was established when Cheyenne County was divided into five counties. Banner County received its name because the original founders of the county wanted it to be the banner county of the state.
In May, 1889, Harrisburg was platted and the following year a courthouse was erected. Settlers continued pouring into the county as it is believed that as many as 4,000 persons lived in the county in the early 1890s. The wave of immigration ceased after 1893 as a severe drought hit the area which resulted in people moving away by the dozens.
By 1900 the county's population had declined to 1,114. The Kinkaid Act of 1904, however, made it possible for persons to homestead a full section of land. This resulted in the population nearly doubling over the next twenty years as the county population was just over 2,000 in 1920. This, though, was the peak of Banner County's population during the 20th century as the population has declined every decade since 1920.
Oil was discovered near Harrisburg in 1951 and provided an economic stimulus to the county. By 1960 over 7,500,000 barrels of oil were produced annually from nearly 400 oif wells in the county. Nearly haif of the county's economy was in oi production. Oil production in the county, however, declined rapidly after 1965. Under 800,000 barrels were being produced annually by 1975.
In 1963, the United States government ordered the development of nuclear missiles sites in the area. Twenty missile sites were built in the county during the decade and are all still active.
Today Banner County is primarily an agriculturally based county. Oil production still plays a small role in the county, but livestock, corn, wheat, and alfalfa are the primary products produced in the county.