Ellensburg is a city in and the county seat of Kittitas County, Washington, United States. It is located just east of the Cascade Range at the junction of Interstate 90 and Interstate 82. The population was an estimated 21,111 as of 2019.

The city is located along the Yakima River in the Kittitas Valley, an agricultural region that extends east towards the Columbia River. The valley is a major producer of timothy hay, which is processed and shipped internationally. Ellensburg is also the home of Central Washington University (CWU).

Ellensburg, originally named Ellensburgh for the wife of town founder John Alden Shoudy, was founded in 1871 and grew rapidly in the 1880s following the arrival of the Northern Pacific Railway. The city was once a leading candidate to become the state capital of Washington, but its campaign was scuppered by a major fire in 1889.