When first posted as such in January 1964, SR 526 began at Jct Sr 525 near Downtown Mukilteo and headed east via Mukilteo Blvd to Everett and ended at Jct US 99. In the late 1960s, a freeway was built heading west from I-5 at Exit 189 to the then new Boeing 747 plant at the north end of Paine Field. SR 526 was shifted to this freeway and the connecting road extending west to SR 525. Today, SR 526 is 4.52 miles long.
Before 1964, SR 526 had been part of SSH 1I.
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