Last name: Delong
This ancient surname can be of pre 7th century Norse-Viking, Old English, French, Norman-French or even Gaelic origins! Recorded in the spellings of Long, Lang, Delon, Delong, Lange, and even Lung, it has at least three possible sources, each with its own meaning and derivation. Firstly it may be a descriptive nickname for a tall person, deriving from the Olde English pre 7th Century "lang", or the Ancient French "long", and mean long or tall. Secondly it may be topographical for one who lived at a long place, and can be either English or French. In this case Long or Delong would refer to a strip of agricultural land within an uncultivated forest as shown by the first recording below. Thirdly it may be of Gaelic (Scottish-Irish) origins, where the modern spelling is usually an anglicization of O'Longain, composed of the elements "O", meaning male descendant of, plus "Longain" a personal name probably derived from "long", tall (as above), or possibly from the homonymous "long", meaning a ship and so possibly a byname for a seafarer, or a Viking, one who sailed in a long-ship. Early recordings include Leofwine Lange, who was noted in the 1070 Anglo-Saxon Chronicle, and Berard Long, recorded in the Feudal Documents of the Abbey of Bury St. Edmunds, Suffolk (1121 - 1148). One of the earliest settlers to New World of the American Colonies, was Henry Long, aged 21 yrs., who embarked from London, England, on the ship "Hopewell", on February 15th 1634. The first recorded spelling of the family name is shown to be that of Aetheric des Langa, which was dated 972 a.d, in the "Old English Bynames" register for Northamptonshire, during the reign of King Edgar of England, who reigned from 959 - 975. Surnames became necessary when governments introduced personal taxation. In England this was known as Poll Tax. Throughout the centuries, surnames in every country have continued to "develop" often leading to astonishing variants of the original spelling.
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As far as I have been able to determine, DeLong is a New World name of Dutch origin (as suggested below) . The person most likely connected to this seems to be Arie Fransen Delange who is noted in New Amsterdam records as using the name Delong.
In Europe, DeLong is known to be of Dutch origin, not French. This is similar to my family history where we used to be DeLange (sounds similar to DeLong), and how many of the Dutch immigrants were placed under DeLong.