I discovered a Phillip Clerkin in Peoria, Illinois that was a baptism sponsor for a child of Patrick Clerkin and Susan McQuillan Clerkin. I have assumed Patrick and Phillip were brothers. I have no other information regarding Phillip, however I believe the descendants of Patrick and Susan live in the Chicago area today.

I'll be happy to share any other information if you are interested. I have a family tree for Susan and Patrick and their children. If you would like more, please feel free to contact me at: jmcquellon@gmail.com
cheers
Jack