Leitrim-Roscommon

I think my Christopher Garrahan (B.abt 1828) ancestor's parents were Murty Garrahan and Margaret Lawlor. We always thought Christopher came from Roscommon. All I know is that a Murty Garrahan was in the Longford Militia Muster in 1814. If anyone has any info on Murty, Margaret and Christopher, I?d l...