Penny's last name has apparently been revealed as "Johnston", but I can't find any references on the matter. I left a comment on the Penny's page asking for someone to cite a reference, but no one has answered as of yet. Unless it's been revealed in accessible episode transcripts, and I just don't know about it. Suggestions?
Yes, I have have been watching TBBT since the beginning and I am positive they have NEVER mentioned it and it has really been bugging me. I have heard rumour that it is Johnston and Longbottom...I'm sorry if this wasn't very helpful I just wanted to state my opinion!!!!!!