Area code 509 is the telephone area code in the North American Numbering Plan (NANP) for the eastern part of the U.S. state of Washington. The numbering plan area (NPA) roughly comprises the state east of the Cascade Mountains, and includes Spokane, the Tri-Cities, Ellensburg, Yakima, Walla Walla, Wenatchee, and Stevenson at the south west. The area code was assigned in a split of area code 206 in 1956.