Comedy Central’s longest-running cartoon returns this month to start its fifteenth season. The first of seven new South Park episodes will air on April 27th.

South Park creators Matt Stone and Trey Parker are contractually obligated to produce at least one more season for Comedy Central. Fourteen episodes will air in 2011, with the trailing seven likely coming in their usual timeslot this fall. This will bring the total number of South Park episodes to 223.

Despite a rise in adult cartoons and general imitators, South Park has remained at the top of the cable ratings game and is consistently Comedy Central’s most-watched show. While the network has aired dozens of animated shows in its 21-year history, only South Park, Ugly Americans and Futurama (which was picked up after Fox cancelled it) remain.

South Park scored 3.7 million viewers for its 14th premiere, and kept an average of 3 million throughout the season. Last year continued the show’s mix of fantastic and topical subjects, including medicinal marijuana, Facebook, Jersey Shore and Inception. There were also two-episode arcs, surrounding H.P. Lovecraft’s Cthulhu monster and the show’s 200th episode.

The shows leading up to South Park‘s 200th episode caused a media storm mirroring the Muhammad controversy in the show’s 2006 episode “Cartoon Wars”. Comedy Central refused to air a depiction of Muhammad after a group of Brooklyn, New York Muslims published terrorist threats on their website. In the second episode, the network even censored the prophet’s name and Kyle’s customary closing monologue.

Comedy Central faced harsh backlash for the decision from free speech advocates in the US. After the network refused to allow the episode to air online or in repeats, Matt Stone and Trey Parker issued a press release about the censorship, placing the future of South Park on Comedy Central in question:

“In the 14 years we’ve been doing South Park we have never done a show that we couldn’t stand behind. We delivered our version of the show to Comedy Central and they made a determination to alter the episode. It wasn’t some meta-joke on our part. Comedy Central added the bleeps. In fact, Kyle’s customary final speech was about intimidation and fear. It didn’t mention Muhammad at all but it got bleeped too. We’ll be back next week with a whole new show about something completely different and we’ll see what happens to it.”

Both episodes were nominated for the Emmy Award for Outstanding Animated Program (an award South Park has won four times). They will appear in the forthcoming Season 14 DVD release, though it’s not known whether the censorship will still be in place.

The events surrounding the controversial Muhammad episodes beg the question: is it time for South Park to end? The show has changed the game for adult animation over the last fourteen years, pushing the boundaries of censorship and cultural satire. Now that South Park has found the line that Comedy Central won’t cross, should the series conclude once its contract expires?

I think so. I’m a big fan of South Park, but even the most faithful of viewers would admit that the quality of the comedy has degraded in the last few years (see The Simpsons and Family Guy for similar lackluster seasons). The last two seasons in particular have been far more about shock laughs than topical observations or organic humor.

That said, South Park is the only creation of Stone and Parker that’s managed to secure a lasting foothold in popular culture. Movies like Baseketball and Team America World Police failed to cultivate the same uproarious response.

If the creators have finally had enough of Comedy Central, expect South Park to move to another cable network, or possibly to an Internet platform (all episodes of the show air for free on its website). In the meantime, fans can enjoy at least one more season on the show’s current home.

South Park airs Wednesday nights at 10PM on Comedy Central. New episodes begin April 27th.

Follow Michael on Twitter: @MichaelCrider