Jerry Seinfeld is Jewish. He has been reported as a convert to the Church of Scientology, but the extent of his involvement with that denomination and whether or not he is actually a member is not entirely clear.
From: Tilman Hausherr, scientology celebrities FAQ" of alt.religion.scientology, last updated 1 July 2005 (http://home.snafu.de/tilman/faq-you/celeb.txt; viewed 11 November 2005):
Name: Jerry Seinfeld
Status [in Scientology]: ?
Sources [confirming that he is/was in Scientology]:
-Seinfeld: The Making of an American Icon by Jerry Oppenheimer
-Playboy 10/93: "I took a couple courses a number of years ago that thought were fabulous. I learned a lot and I had a good experience with it."
-WP [apparently Wasington Post] 16.4.1998: "I think the stuff I learned there really did help me a lot," he said. When reminded then that Time magazine had just run a cover story about Scientology that included charges it was a "thriving cult of greed and power" and a "ruthless global scam," Seinfeld scowled and dismissed the article as "poor journalism."
...From Premiere 9/93 [with comments from Factnet & L. Wollersheim]: ...People who have drifted through Scientology include Jerry Seinfeld, Patrick Swayze...