Apparently there was an earlier wave of Irish that came to America a couple of decades before the famine. This exodus seems to have been prompted by changes in laws by the British that devasted those who made their living raising sheep. I would guess the large number of Garveys and McGarveys in Pennsylvania and Ohio were part of this wave of Irish immigrants - and had probably come from the northern part of Ireland.

Keep in mind that each colored circle represents " a Garvey" - sometimes it's a whole family, while other times it's just an individual. The positions of the circles are only meant to indicate county of residence. A large circle containing a number is used in the cases where the number of Garveys in one place is too large to represent with individual circles (for example: Cleveland in 1870).