[7] A concurrency with SR 260 travels northeast into Adams County parallel to the Columbia Plateau Trail in the Palouse before entering Washtucna and being designated as Main Street.

SR 261 continues north into farmland and crosses the John Wayne Pioneer Trail in Ralston before its northern terminus at a diamond interchange with I-90 and US 395 southeast of Ritzville, becoming Division Street as it serves the city.

[10] The Mullan Road was constructed in 1862 and crossed the Snake River with a ferry crossing at Lyons Ferry until the construction of the Lower Monumental Dam downstream caused the water level to rise and longer wait times, resulting in the reconstruction of the Snake River Bridge.

[11][12][13] The current route of SR 261 from Washtucna to Ritzville was designated during the creation of the Primary and secondary state highways in 1937 as SSH 11E.

[14][15] A branch of SSH 11B was added in 1957 that extended from Washtunca to US 410, later an extension of US 12,[16] east of Starbuck with an un-built bridge over the Snake River at Lyons Ferry.