The MUNSON surname in the USA is most commonly found in the descendants of Thomas Munson of New Haven and Rattlesden, County Suffolk, England in the 1600s. See the Thomas Munson foundation web site at [http://www.thomasmunson.org/about_tm.asp]
Other bearers of the surname typically are of Scandinavian descent as Monsen (son of Mons) sounds like Munson and was often spelled that way on emigration to the USA. There are some Norwegian Munsons (see [http://kittymunson.com/index.php?page=munson] ) and Danish Munsons and probably others.