The North Fork of the Nooksack River is the northernmost river in Washington State. It is located on the western slope of the North Cascade Mountains and runs east to west near the Canadian border. Here we report the findings of a lichen and allied fungi survey of the valley bottom conducted in 2019. One hundred and forty-five species were documented from 69 genera, increasing the number of species known from this area to 153 in 71 genera. Six species are reported for the first time from Washington State: Abrothallus santessonii (D. Hawksw.) Suija, D. Hawksw. & Pérez-Ort.; Gyalectaria diluta (C. Björk, G. Thor & T.B. Wheeler) Schmitt, T. Sprib. & Lumbsch; Lecanora thysanophora R.C. Harris; Lepraria nivalis J.R. Laundon; Multiclavula mucida (Fr.) R.H. Petersen; and Sarea difformis (Fr.) Fr. The bottom of this valley, like many others in the region, has been heavily disturbed by timber harvesting, development, and recreational use. Despite these impacts, we show that this area is still important habitat for lichen biodiversity, including rarities.