Secondary State Highway 1A

When first added to the state highway system in 1937, SSH 1A began at Jct PSH 1 (US 99) at Blaine and headed east via Lynden to a junction a few miles SW of Sumas, then south to a junction with the Austin Pass (Mt Baker Hwy) branch of PSH 1 (now SR 542) at Lawrence (Nugents Corner). SSH ran coincident with PSH 1 in a southeasterly direction to Deming, then left PSH 1 and headed south to Sedro-Woolley, Arlington, and Snohomish, ending at Jct PSH 2 in Woodinville. A branch of SSH 1A headed NE from the SSH 1A trunk SW of Sumas to Sumas.

In 1951, SSH 1A was realigned between Lynden and Nooksack. From Lynden, SSH 1A was routed south on SSH 1B across the Noocksack River, then east via Everson to Nooksack. The Sumas branch was extended south along the former SSH 1A trunk to Nooksack.

In 1953, SSH 1A from Blaine to SSH 1B was dropped from the state highway system.

The southern terminus of SSH 1A was shifted from Jct PSH 2 in Woodinville to Jct PSH 15 Bothell Monroe Branch (now SR 522) north of Woodinville in 1965.

Today, SSH 1A from Sumas to the Woodinville area is SR 9. The east-west section of SSH 1A from Jct SSH 1B (now SR 539) via Everson to Nooksack is now SR 544.