Conodont faunas from the March and Oxford Formations of the Brockville area, southeastern Ontario, are described. The specimens are assigned to fifteen species comprising eight genera.The Nepean sandstone, at the bottom of the Paleozoic section, has a thick conglomerate at its base; the overlying sandstones are burrowed and probably of marine origin.Basal March sandstones are blue–gray in color and have been extremely bioturbated. The higher standstones are orthoquartzites with minor burrowing. Both are probably offshore deposits.The Oxford Formation comprises sandy limestones and dolomites as the dominant lithologies. It was probably deposited on a tidal or intertidal flat.The conodont faunas indicate that the March Formation is probably late Tremadocian in age, and that the Oxford Formation is Arenig in age. The Nepean sandstone yielded no conodonts.The March and Oxford conodont faunas are correlated with those from the Columbia Icefields section, Alberta; the House limestone, western Utah; the El Paso Formation of Arizona; the Oneota and Shakopee Formations of the Upper Mississipi valley; and the St. George Formation, Newfoundland.Genera of European affinity are absent and a closer tie with contemporaneous continental North American faunas is suggested.The oldest occurrence of the genus Strachanognathus in this region is noted.