I haven't examined Griffith's directly, but I do have a printout from a website that has a database of all the information in it.It shows that McEntees are very concentrated in Monaghan (34 households) and Meath (23 households). All the other McEntees are more scattered.
Why do you happen to call Monaghan "northern Ireland"?I ask because I just found some anomolous information (in terms of what I've heard) that my McEntees may have come from Northern Ireland.The 1930 Census differentiated between Northern Ireland and the "Irish Free State": Ireland having become independent in 1921.On that census, my g-GM McEntee is shown as from Northern Ireland. (Also her husband, Frederick Dunne). This was contrary to anythng my mother has heard.(But Monaghan belongs to Ireland, not Northern Ireland.)