SR 251 was originally a county road until 1913, when it was added to the state highway system, but was later removed.

The highway turned north from SR 25 and followed the Columbia River upstream as well a railroad owned by the Kettle Falls International Railway.

[4][5] The highway traveled northeast, then east through a series of hairpin turns before turning north to Boundary, an unincorporated community in Stevens County, where SR 251 entered Canadian customs and continued into British Columbia as British Columbia Highway 22A (BC 22A).

[20] In 1983, SR 251 was removed from the state highway system and control was relinquished to Stevens County.

[2][3] After it was turned over, Stevens County continues to maintain the roadway and no realignments or significant events have occurred.