The largest city and seat of Benton County, and a shipping point for cattle and sheep; also dubbed the birthplace of Washington’s wine industry. It was an Indian camp during salmon runs in the river. The first settler, James Kinney, homesteaded in 1880. Several names have been given to the place including Yakima Falls, and later, Prosser Falls. At one time, it was known as Cook’s or Colonel Cook’s Ferry. In 1884, the first post office was named Lone Tree, from Lone Tree Landing on the south side of the river, where a single, old cottonwood tree once stood. On January 26, 1885, a town site plat was filed by Col. William F. and Flora T. Prosser. In the same year, the present name was given by Northern Pacific Railway officials when their line was built, naming the station for the Prossers. The advent of the Northern Pacific, and subsequent development of the power site at Tap-Tap Falls between 1890–94, lent impetus to the town’s growth. A new county courthouse was built in 1926 at a cost of $100,000.
On the bank of the Yakima River, with the Horse Heaven Hills rising behind it toward the south, Prosser is a solidly built little town, with a busy flour mill and dehydrating plant. An annual event is States’ Day, held early in December, originally an occasion for assembling of emigrants from eastern parts of the United States.
Today this is known as the Family Christmas Festival and includes the annual lighting of the Christmas tree with carolers and holiday music. In the fall, the city hosts the annual Harvest Festival and Great Prosser Balloon Rally, launching hot air balloons at dawn from the Prosser Airport.