Jeff Yagher is the John Germaine in The Rye (Season 7 Episode 11).
Jesee D. Goins is Cop in 
Jesee White is Ralph in 
Jeffrey von Meyer is Poker Player #4 in The Opposite (Season 5 Episode 13).
Jennifer Campbell is Tia Van Kamp in three episodes. The first The Airport (Season 4 - Episode 12).
Jennifer Coolidge is Jody, Jerry's girlfriend in The Masseuse (Season 5 Episode 9).
Jeremiah Birkett is Jean-Paul (or Jean-Paul Jean-Paul), the runner from Trinidad and Tobago in The Hot Tub (Season 7 Episode 5).
Jerry Levine is the stationery store guy in The Big Salad (Season 6 - Episode 2).
Jerry Stiller is Frank Costanza, George's father in 27 episodes. His first appearance was in The Handicap Spot (Season 4 Episode 22).
Jessica Hecht is Lindsay Enright in The Couch (Season 6 Episode 5) and in The Gymnast (Season 6 Episode 6).
Jessica Lundy is Naomi in The Watch (Season 4 Episode 6) and in The Bubble Boy (Season 4 Episode 7).
Jill Gray Savarese is Kissing Medical Intern in The Junior Mint (Season 4 Episode 20).
Jill St. John is Mrs. Abbot (Mickey's mother) in The Yada Yada (Season 8 Episode 19).
