It's curious that this show was able to last 5 seasons with a supporting cast that was really more recurring than truly supporting: Bernie Koppell said plainly that he never had an actual contract to do this show or any of the others he was in at that time. Lew Parker was only on occasionally (though I think his appearances increased as the seasons went on), Rosemary DeCamp, Bonnie Scott, Ruth Buzzi and Dabney Coleman kind of came and went. I'd consider all of these people to have been recurring rather than regular supporting players.

Yeah, Ann's father was the main recurring character, to me. Bernie Koppel did pop up some also through the seasons.

Now that you mention the lack of regulars, there was always a different actress playing Ann's-female-friend-next-door. Ruth Bauman was played by three actresses (one with a different first name, Margie), Bonnie Scott as Judy was in only 19 episodes. Ruth Buzzi, only a few; unclear if she was a neighbor.

Lew Parker was superb in his part, and was part of quite a few memorable episodes. He was in 65 episodes.