UPDATE: Stan Marsh, Kyle Broflovski, Eric Cartman and Kenny McCormick are set to come back on "South Park" season 19 premiere on Sept. 16.
Both "South Park" and "Arthur," two of the longest-running animated series in the United States, are about to enter season 19 but their premiere dates are yet to be confirmed.
"South Park" season 18 ended on Dec. 10, 2014 with episode 10 titled "#HappyHolograms." On the other hand, "Arthur" season 18 will end on May 12 with episode 10 titled "Shelter From The Storm: Part 1 And Part 2."
Because its season 17 premiered on Sept. 25, 2013 and its season 18 premiered on Sept. 24, 2014, "South Park" season 19 is reported to premiere on Sept. 23.
There is still no official premiere date for "Arthur" season 19 but it is said to be in 2016.
Created by Matt Stone and Trey Parker for the Comedy Central television network, "South Park" debuted on Aug. 13, 1997 with an episode titled "Cartman Gets An Anal Probe." The show is the third longest-running animated series in the U.S. with 257 episodes aired.
On Nov. 16, 2011, Comedy Central president Michele Ganeless confirmed that "South Park" will be renewed for three more seasons, which means it will still have at least season 20 in 2016, according to Collider.
"Arthur" is created by WGBH and Cookie Jar Group for the Public Broadcasting Service (PBS). It eventually became a co-production between WGBH and 9 Story Entertainment Inc. from season 16 to present. Its first season's first episode aired on Sept. 2, 1996, making it the second longest-running U.S. animated series. It currently has aired a total of 211 episodes.
The longest-running animated series in the U.S. is "The Simpsons," which has aired 571 episodes since it debuted on Dec. 17, 1989. It was created for the Fox Broadcasting Company by Matt Groening. One of the show's developers, Sam Simon, died of colon cancer on March 9.