State Route 528

When the current state highway numbering system was first posted in January 1964, SR 528 Began at I-5 exit 199 and headed east to State Street in Downtown Marysville. SR 528 was designated by law as a state highway extending east from Marysville to Jct SR 9. There was still a missing gap east of Marysville, however, so the SR 528 route markers stopped at State Street.

State Street had been US 99 before the Marysville Bypass, now I-5, was constructed in the mid 1950s. A spur of SR 528 extended south on State Street to I-5/US 99 south of town.

In 1969, I-5 was completed from Everett to the south end of Marysville. That same year, US 99 was dropped from the US highway system in Washington State. Former US 99 from Exit 192 through Everett to the south end of Marysville became signed as Business Loop 5. In 1971, Business Loop 5 became SR 529. The 529 designation also replaced the SR 528 spur along State Street in Marysville.

Finally, in the 1980s the missing gap in SR 528 east of Downtown Marysville was filled in and SR 528 signs were posted all the way from I-5 to SR 9. Today, SR 528 is 3.46 miles long.

Before 1964, SR 528 had been the Marysville branch of PSH 1.