It originates as a toponymic surname from any of various places called "Langdon" or similar in England, such as in the counties of Devon, Dorset, Essex, or Kent. The name ultimately derives from the Old English lang, meaning "long"; and dun, meaning "hill". Notable people with the surname include:Charles C. Langdon, American politician
Chauncey Langdon (1763–1830), American politician, lawyer and judge
Craig Langdon, Australian politician
Text adapted from Wikipedia, CC BY-SA 4.0. Photograph: kallerna (see Commons), Wikimedia Commons.