SR 528 is 3.5 miles (5.6 km) long and lies entirely within the city of Marysville in northern Snohomish County.

[4] The highway travels east into downtown Marysville on 4th Street, crossing over a section of the BNSF Railway's Bellingham Subdivision (which also carries Amtrak's Cascades passenger trains) near Comeford Park and the city's landmark water tower.

[3][8] The highway continues east on 4th Street and crosses Allen Creek, a tributary of Ebey Slough with large wetlands.

[17] The state government widened the westernmost 1⁄2 mile (0.80 km) of SR 528 between I-5 and Columbia Avenue to 60 feet (18 m) and installed traffic signals in 1972.

[19] A connection for the two sections of SR 528 was planned in the late 1960s by the state government and approved for construction in 1969,[18] but was delayed until the 1980s due to a lack of available funds from a federal program.

[24][25] The I-5 interchange in downtown Marysville was expanded in the 1970s and rebuilt in 1993 with wider ramps and a new traffic signal, funded by a federal grant.

[28] The westernmost section of the highway through downtown Marysville was rebuilt in 2008 as part of a repaving project that also replaced a set of water mains.

[33][34] The I-5 interchange is planned to be partially rebuilt in the late 2020s to address congestion and allow for free right turns on red from the northbound ramp.

[35] A long-term plan from WSDOT and the Tulalip Tribes proposes adding a set of roundabouts to replace the traffic signals in and around the interchange.