We estimated the population size of McKay's Buntings (Plectrophenax hyperboreus) from surveys across their restricted breeding range on St. Matthew and Hall Islands, Alaska (326 km²). We used a multimodel approach to (1) estimate population size from counts with distance sampling, and (2) account for the effects of observers, habitat, flock size, and date on detectability. We counted 2400 buntings along 202 km of transects; most birds were in tundra (44%) or rocky uplands (46%). Breeding density was higher on Hall Island (154 ± 20 [SE] birds km⁻²) than St. Matthew Island (93 ± 7 birds km⁻²), possibly due to differences in habitat. Population size was 31 200 ± 2000 birds (CI_95% = 27 500–35 400 birds), 5–11 times greater than previously reported, but still small among North American passerines. Populations of this species should therefore be closely monitored and the focus of conservation.