[3] According to the United States Census Bureau, Pomeroy has a total area of 1.78 square miles (4.61 km2), all of it land.

Captain Benjamin Bonneville also passed through the future site of the town while he was surveying for the US government in 1834.

In 1860, an Irish settler named Parson Quinn settled just east of present-day Pomeroy, and lived there for the next 40 years.

Rancher Joseph M. Pomeroy purchased the land in 1864,[5] and platted the town's site in May 1878.

[8] The debate continued through both houses of the Washington Territorial Legislature in for the remainder of 1883 to Governor William A. Newell of the Washington Territory, and eventually reached the United States Congress in 1884.

[5] Despite a city ordinance which mandated fire-proof materials for downtown buildings after fires in 1890 and 1898, on July 18, 1900 a blaze destroyed half of the small town's business district.

The prohibition quickly led to rampant bootlegging and corruption which lasted until the 21st Amendment passed in 1933.

34.0% of all households were made up of individuals, and 19.4% had someone living alone who was 65 years of age or older.

Pomeroy, as is typical for this region, has a borderline Mediterranean/continental Mediterranean climate (Köppen Csb/Dsb) with dry summers featuring warm to hot afternoons and cool to warm mornings, and chilly, cool, or cold and snowy, if not severe, and wetter winters.

Annual events hosted by the Pomeroy Chamber of Commerce include the Pioneer Day and Tumbleweed Festival held the second weekend in June, the Garfield County Fair in September, and the Starlight Parade and Festival of Trees which begins after Thanksgiving.