Via ComicBook, in a recent interview with Jon Regan on his podcast, actor John Witherspoon, the voice of Grandpa on The Boondocks, says the show is currently producing a 5th season.
“I’m on the cartoon—what is it? ‘The Boondocks?’ I didn’t change my voice for ‘The Boondocks,’ and they coming back. ‘The Boondocks’ is coming back … It’s one of the best cartoons I’ve ever been on.” – John Witherspoon on The Joe Regan Experience
Adult Swim has yet to confirm or announce if this is true or if creator Aaron McGruder will be involved or not.