Well, to make a long story short, Matt Stone is Jewish!
Since Matt Stone's mother is Jewish, and in Orthodox Judaism and Conservative Judaism, those with a Jewish mother (or those who underwent a halakhic conversion) are considered Jewish, then that makes him Jewish. His father is not Jewish.
Matt Stone (whose full birth name is Matthew Richard Stone) was born on May 26, 1971 in Houston, Texas, U.S..
He is best known for being the co-creator of South Park along with his creative partner and best friend Trey Parker, as well as co-writing the 2011 multi-Tony Award winning musical The Book of Mormon.
If you see any details that require update, please Let us know!