The first posting on this thread regarding a Patrick Halpin b about 1842 - who moved to Lancashire and had a father Patrick, seems to have been overshadowed by the second query about a family with the same surname who moved to USA (as far as I can tell).
So returning to the original query -- there is a Patrick Halpin baptised on 13 March 1842, but in Drumcanrath, County Meath.
Father Patrick Halpin, mother Bridget Shekey. (Sponsors Michael and Mary Shekey)
In addition;
Peter Halpin, baptised 17 Jul 1848 also in Drumconrath, County Meath. Father Patrick - mother Bridget Sheeky. (One of the Sponsors - Catherine Sheeky).
I cannot see a baptism for a John at the correct time though.
My Westmeath ancestors moved to Westmeath from County Meath -- so this family MAY have done the same thing and may just be worth considering.