First found in Bavaria, where the name was closely identified in early medieval times with the feudal society which would become prominent throughout European history. The name would later emerge as a noble family with great influence, having many distinguished branches, and become noted for its involvement in social, economic and political affairs. Like many surnames, the name Dahn began as a personal name and was later adopted as a surname. It is a shortened form of the Germanic personal name Deinhard, which is made up of the words "degen," meaning "warrior or hero" and "hard," meaning "brave or strong."

Some of the first settlers of this family name or some of its variants were: Maria Dahn, who came to Nova Scotia in 1757 and Georg Henrich Dehn, who settled in Pennsylvania in 1772.

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