They are found throughout the Americas, hence the common name American cormorants.

A molecular phylogenetic study of the cormorants published in 2014 found that these three species formed a clade that was sister to the genus Leucocarbo.

[1] To create monophyletic genera, the three species were moved the resurrected genus Nannopterum that had been introduced in 1899 by English ornithologist Richard Bowdler Sharpe to accommodate the flightless cormorant.

[2][3][4] The genus Nannopterum is thought to have split from Leucocarbo between 6.7 - 8.0 million years ago.

Genetic studies have found that the neotropic and double-crested cormorants form a clade with the flightless cormorant, and they are thus placed together in the genus Nannopterum despite both species having normal-sized wings and full flight capabilities.