John Mahady 1845 : Short Biography

I am searching for information on John Mahady born between 1841-1845 in or near Rathowen, Westmeath. John Mahady immigrated to the US when he was between 11 and 14 years of age. My grandfather said he stayed with relatives in New York, but was unsure who they were. His parents were Michael and Rose (Whalen) Mahady. Per a San Francisco publication, he was born in 1845; however, the Rathaspick and Russagh parish records seem to be missing for that period. I found birth and baptismal records for two his older siblings, Patrick Mahady (b 1837)  and Mary (b 1844). He fought in the US Civil War on the Union side and gave his birth year as 1841, which may have been due to a minimum age enlistment requirement, but does create some question.

Any information on the family Mahady (possible alternate spellings: Mahedy, Mahaddie and Mahidy) in the Counties Westmeath or Longford would be helpful. I believe most of his immediate family may have mimmigrated to either the US or UK sometime in the late 1850's. 

Thank you, 

Linda