Native American cultures in the area included the Interior Salish, Wenatchi, and Okanagan.

The first white settlers began to arrive in the mid-to-late-19th century, primarily with the goal of raising livestock.

One government official described the area in 1879 as, "…a desolation where even the most hopeful can find nothing in its future prospects to cheer.

"[4] When railroads arrived they also brought new settlers, and the economy began a shift from ranching to dryland farming.

This transition required the people to have ready access to water, and irrigation became a necessity.

With the influx of dryland farming, the county soon boasted access to three major railway systems; the Great Northern Railway, Northern Pacific Railroad and the Chicago, Milwaukee & St. Paul Railroad.

The Washington State Legislature officially created Grant County on February 24, 1909, naming it in the memory of Ulysses S. Grant, the 18th president of the United States, and a major contributor to the Union victory in the American Civil War.

The Columbia Basin Project, which ultimately produced the Grand Coulee Dam with its associated irrigation and hydroelectric generating grid, was an outgrowth of the 1902 creation of the United States Bureau of Reclamation.

The environmental climate of Grant County is characterized by hot summers and cold winters.

Grant is the #1 crop-producing County in the State, producing a large part of the Washington hay harvest.