Today, alligatorines can be found in the southeastern United States and in a very restricted area of the Yangtze River Valley in China. In the recent past, Chinese alligators ranged throughout more of China, but habitat loss has resulted in them being almost completely extinct in the wild.
In the past, alligatorines lived in a much wider area, with fossils found in the continental US, Canada (even Ellesmere Island), several western European countries, China, Taiwan, Thailand, and another place I’m not going to disclose because it’s someone else’s research and hasn’t been presented yet.
This trio of modern continents–North America, Europe, and Asia–used to make up a large supercontinent called Laurasia. During the course of Laurasia’s history, various parts have been separated as islands (especially true in Europe), and entire continents have been connected and disconnected as land bridges appeared and disappeared.
By the time alligatorines evolved, Laurasia was no longer one big mass, but given the continued close association between the continents, it’s still useful to think of alligatorines as having a Laurasian distribution.