Before 1964, the route from Newport to BC 6 was the northernmost section of Primary State Highway 6, which ran from Spokane to BC 6. Originally created in 1964, SR 31 extended southeast to an intersection with U.S. Route 2 (US 2, formerly US 195) in Newport. The North Cascades Highway (SR 20) was extended to Newport in 1973 and SR 31 from Newport to Tiger became SR 20. SR 31 had one auxiliary route, SR 311, which became SR 211 after SR 20 was extended.