The Iago sparrow was first collected by Charles Darwin during the first stop of the second voyage of HMS "Beagle" at the island of Santiago (St. Iago). It was described for him in 1837 by zoologist John Gould, in the "Proceedings of the Zoological Society of London", and given the name of "Pyrgita iagoensis". By the time Gould wrote "The Zoology of the Voyage of H.M.S. Beagle" with Darwin and three other zoologists in 1841, he had placed the Iago sparrow in the genus "Passer", where it remains. The genus, among the sparrows of the Old World in the family Passeridae, also contains at least 20 other species, among them the house sparrow and Eurasian tree sparrow.