State Route 10 is part of the original roadway of U.S. Route 10, which ran from Detroit, Michigan to Seattle from 1926 to 1969. Today US 10 only runs from Bay City, Michigan to West Fargo, North Dakota, with Interstate 94 and Interstate 90 replacing it throughout most of the West. In Washington, I-90 now occupies most of US 10's old routing; SR 10 is one of a number of short segments of the original routing that diverge from the interstate in places, and is the only one to inherit the old U.S. highway's numeric designation.
Milepost numbering on SR 10 is derived from the numbering used on US 10 when it originated in Seattle: posted mile markers along the 16-mile highway begin with milepost 89 near its northwest terminus and end with milepost 104 in the southeast. This also means that the mileposts on SR 10 are closely aligned with the mileposts on nearby Interstate 90; e.g., SR 10 milepost 92 is just across the Yakima River from I-90 milepost 92.