Secondary State Highway 1B (Washington)

State Route 539
Map of western Whatcom County in northwestern Washington with SR 539 highlighted in red
Route information
Auxiliary route of I‑5
Defined by RCW 47.17.785
Maintained by WSDOT
Length:	15.16 mi (24.40 km)
Existed:	1969 – present
Major junctions
South end:	I‑5 in Bellingham
	SR 546 in Lynden
North end:	BC 13 near Langley, BC
Location
Counties:	Whatcom
Highway system
State highways in Washington Interstate US State Scenic Former PSH 1964 renumbering Former ← SR 538 SR 542 →

State Route 539 (SR 539), named the Meridian Street in Bellingham, Guide Meridian Road elsewhere, and commonly known as The Guide, is a state highway in Washington, United States. It runs for 15.16 miles from Bellingham in the south to the Canada–US border at Lynden-Langley in the north. The road is so named because it follows the Guide Meridian between R2E and R3E, 12 miles east of the Willamette Meridian.

SR 539 begins at Exit 256 of Interstate 5 just south of the Bellis Fair Mall, approximately four miles north of downtown Bellingham. From there it proceeds due north to the Canada–US border between Lynden and the Township of Langley, British Columbia.

Once past the Bellis Fair Mall immediately north of the I-5 interchange, SR 539 continues through the shopping centers of the northern outskirts of Bellingham; Whatcom Community College and the Cordata Business Park are also nearby.

North of Bellingham, it passes through the small town of Laurel, which contains Meridian High School. It then passes over Wiser Lake and the Nooksack River, before arriving in Lynden, home to a municipal airport. At Lynden it changes from 4 lanes to 2 as it proceeds north to the border near Aldergrove, British Columbia, Canada.