SR 261 starts at Jct US 12 at Delaney and heads NW via Starbuck and Lyons Ferry to Jct SR 260 at McAdam. From McAdam, SR 261 runs coincident with SR 260 to Jct SR 26 at Washtucna. The highway from McAdam to Washtucna is only sighned as SR 260. The state was going to build a more direct SR 261 alignment from the Palouse Falls area to Washtucna but never did. This more direct alignment might never be built, leaving a gap in SR 261 signage between McAdam and Washtucna.
At Jct SR 26, SR 260 ends. SR 261 heads north via Ralston and ends at Jct I-90 in Ritzville. SR 261 is 62.71 miles long, including the section coincident with SR 260.
Although SR 261 from Delaney to McAdam had been originally added to the state highway system before 1964 as a branch of SSH 11B, this section of SR 261 neither posted as such nor maintained by the state until the completion of the Lyons Ferry Bridge across the Snake River circa 1968. This bridge had originally been built across the Columbia River at Vantage circa 1926 and had been part of PSH 7, later US 10. When the present I-90 bridge at Vantage was opened to traffic in 1962, the old Vantage bridge had been disassembled and hauled by truck to Lyons Ferry to be used as part of SR 261.
Before 1964, SR 261 from Washtucna to Ritzville had been SSH 11E.
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