Grand Coulee is a city in Grant County, Washington, United States. The population was 972 at the 2020 census. Grand Coulee was officially i…Grand Coulee is a city in Grant County, Washington, United States. The population was 972 at the 2020 census. Grand Coulee was officially incorporated on November 6, 1935. It is located above the Grand Coulee Dam and next to North Dam. It was the birthplace of the molecular biologist John Abelson.