Etna is a borough in Allegheny County in the U.S. state of Pennsylvania, along the Allegheny River, opposite Pittsburgh. Etna was named after the volcano Mount Etna, an allusion to blast furnaces, steel mills, galvanized-pipe works, and other manufacturers located there. In 1900, 5,384 people lived in Etna. In 1940, 7,223 lived there. The population was 3,451 at the 2010 census.