Brewster was officially incorporated on April 29, 1910.

In 1811, David Stewart of Astor's Pacific Fur Company established Fort Okanogan, the first American post in Washington just north of the present site of Brewster. In 1859, the area experienced a gold rush and by 1880, steamboats became a common site on the Columbia River as far north as Brewster. Most of the settlers in the area were cattle and sheep ranchers. The town's location near the confluence of the Columbia and Okanogan Rivers made Brewster the "gateway" to the vast lands of the north. Brewster was founded in 1910 and grew as river travel increased. The coming of the railroad in 1914 opened more opportunities, including mining and logging. The history of the Brewster area is one of the great Indians, of growers who imagined taming the wild country for food production, of railroad men and miners, of daring people building massive dams to harness the wild Columbia River. The land provided something for every dreamer, and still does. The economy of Brewster rests with the fruit industry. There are 4 warehouses that pack several million boxes of fruit annually. The warehouses are supported by thousands of acres of orchards in the surrounding countryside. Every season of the year offers unique recreational opportunities. The Fort Okanogan Interpretive Center near Brewster represents the site of the first inland fur trading post in the state.