The seat of Garfield County and terminus of a branch line of the Union Pacific, this was the center of the surrounding wheat, barley, and cattle country and for the irrigated acreage to the north, where quantities of beans, alfalfa, fruits, and vegetables were produced.

In 1864 Joseph M. Pomeroy came to this region from Ashtabula, Ohio, and started a blooded-stock farm on Pataha Creek, to supply the demand of stagecoach operators. In the late 1870s a flour mill was erected, rail connections were constructed, a bank established, a fire department formed, and the townsite platted. The town was then on the stage route to Lewiston, and old timers spoke of the St. George Hotel, where travelers swapped tall tales and stood each other up for drinks. Several times daily during these boom days six-horse coaches clattered into town, the animals in a lather, and dust clouds flying. In 1882, the town was named seat of the newly formed Garfield County.

During these frontier days Pomeroy was beset with gamblers, road agents, miners, and cattle rustlers. In an effort to maintain order and to control traffic in liquor and drunkenness, the town adopted a local option measure but this was soon declared unconstitutional. Recalling these boom days an old-timer said, “Main Street had 20 saloons and things were poppin’. The town ain’t bigger now an’ nothin’ is poppin’.”

Pomeroy, nevertheless, was a prosperous town with a compact business section, neat, shaded, residential districts, and a city park. Prior to 1864, the land was claimed by Walter Sunderland, who established a stock ranch. On December 8, 1864, he sold out to Joseph M. Pomeroy, who had been a mechanic for Wells, Fargo & Company and was a Civil War veteran. On May 28, 1878, Pomeroy platted the area as a town site and it was named for him. At one time the place supported 20 saloons; while the capacity of early-day miners was prodigious, this number appears to have been somewhat more than one small town could maintain.