Breeding within the Salish Sea by Pelagic Cormorant (Phalacrocorax pelagicus), Double-crested Cormorant (P. auritus) and Brandt's Cormorant (P. penicillatus) was summarized from published and unpublished sources for the 1891–1955 period. None of the 3 cormorant species were recorded breeding in the Salish Sea between 1792 and 1891 although sporadic breeding may have been missed. Pelagic Cormorants were first reported breeding at Mandarte Island, British Columbia, in 1891 and afterwards bred there regularly; by 1955, 22 colonies had formed in the central and northern Salish Sea, including the San Juan Islands (n = 9), Gulf Islands (n = 5), inner Strait of Juan de Fuca (n = 4), and northern Strait of Georgia (n = 4). Before regular breeding by Double-crested Cormorants began at Mandarte Island (1927) and Ballingall Islets (1934), they apparently bred sporadically at St. John's Point (Hornby Island) in the northern Salish Sea (1896) and Mandarte Island (1900). By 1955, 8 colonies had formed in the central and northern Salish Sea, including the San Juan Islands (n = 3), Gulf Islands (n = 3) and northern Strait of Georgia (n = 2). Brandt's Cormorants only bred sporadically in the San Juan Islands at Flattop Island (1928), Matia Island (1940) and Lopez Island (<1953). Evidence of breeding in the central Salish Sea by all 3 cormorant species suggested resettlement of individuals from colonies on the outer west coast of Washington through the Strait of Juan de Fuca. Subsequent expansion by Pelagic and Double-crested cormorants in the central and northern Salish Sea suggested local growth after colonization, although impacts from human disturbance and predators affected certain colonies. Reduced harvesting by the shrinking population of indigenous peoples at cormorant colonies on the outer coast of Washington likely prompted colonization of the Salish Sea.