This interesting surname is of Anglo-Saxon origin, and is a locational name from some minor or unrecorded place, perhaps a "lost" village. There are an estimated seven to ten thousand villages and hamlets that have now disappeared from Britain since the 12th Century; the prime cause of these "disappearances" was the enforced "clearing" and dispersal of the former inhabitants to make way for sheep pastures at the height of the wool trade in the 15th Century, and natural causes such as the Black Death of 1348, in which an eighth of the population perished. The original place is thought to have been situated in the Manchester area of Lancashire. There are no recordings extant of the early forms of the placename, but it is believed to mean "the broad, wide hill", derived from the Olde English pre 7th Century "side", used in the sense of a hill-slope extending for a considerable distance, with "dun", hill, mound. In the modern idiom the surname can be found as Seddon and Seadon. On December 17th 1575, John Seadon was christened at the Church of Leigh, Lancashire, and Peeter Seadon married Hellen Stringfellow on April 22nd 1629, at Warrington, Lancashire. The first recorded spelling of the family name is shown to be that of Roger Seddan, which was dated January 16th 1521, marriage to Elizabeth Greenehalghe, at Manchester, Lancashire, during the reign of King Henry V111, known as "Good King Hal", 1509 - 1547. 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.