The 1850 census of New Haven, Connecticut shows a George Mathingby aged 17 and born England as an apprentice for Thomas Phillips. This looks suspiciously like a Mattingly when viewing the actual census. By 1860 there are several persons named Matthingly in New Haven, all reportedly born in England: Robert 69, Sarah 45, Mary A. 26, John 22, and Arthur 9. I believe these were all Mattingly's.