Apparently there was an earler 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: Philadelphia in 1850).