Cartman's mom is named Liane after Trey Parker's former fiancée. He caught her with another man so he named the promiscuous character after her.
To date South Park still holds the Guiness World Record for "Most Swearing in animated series."
Kenny was going to be killed off permanently in season 5, but Parker and Stone ultimately decided not to since they realized that he was a huge part of the show. He has officially died over 120 separate times.
Stan's dog Sparky, despite not having any dialogue, is played by Oscar winner George Clooney, who is a big fan of the show. Clooney accepted the small role, which he recorded remotely. He was rewarded with a full voice role on South Park: Bigger, Longer & Uncut (1999).
Most of Cartman's lines are ad-libbed by Trey Parker who has stated that Cartman is his favorite character on the show.