There are at least five genetically distinct McGrew lines in the United States. Three genetically distinct lines of McGrew's are descended from individuals who immigrated from N. Ireland, between about 1725-1775. Recent DNA results have shown that Robert McGrew, the ancestor of most 'northern' McGrew's, was related to James A. McGrew who founded a line of 'southern' McGrew's. The other Northern Irish McGrew lines are descended from Thomas McGrew of SC and TN and Patrick McGrew of WV. A fourth McGrew line is descended from Alexander MacGruar/McGrew who settled in South Carolina about 1750. This line is Scots. A fifth line is descended from Andrew McGrew/Megrue of Baltimore and is Norse Viking probably via Scotland.