When the current state highway numbering system was first posted in January 1964, SR 801 started at Jct SR 8 in Rochester and headed NNE to Littlerock, then east to I-5 Exit 95 and ended. US 12 was extended into Washington State in 1967. SR 8 from Elma via Rochester to Grand Mound became part of US 12. Former US 410 from Elma to Mud Bay became SR 8. Because SR 801 no longer connected with SR 8 but instead connected with US 12, SR 801 was renumbered SR 121.
Before 1964, SR 801 had been SSH 1M.
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