I'm sure she must have a surname, I've 'googled' but nothing seems to be coming up.
(other search engines are available)
I'm kicking myself, especially as her 'dad' was in one episode when she and Leonard were pretending to be boyfriend and girlfriend.
Would some please be kind enough to put me out of my curiosity?
wikipedia says " In contrast to all other characters, Penny and her father have not been imbued with a surname, thus far. However, co-creator Bill Prady stated that Penny's last name will be revealed eventually" so it must be true.
her kin are all criminals and drug dealers in omaha nebraska which is why she's in LA but when she marries leonard she'll have to be given a surname for the wedding