The episode, shown in America on Wednesday night on Comedy Central, depicts a bloody Irwin with the stingray that killed him still attached to his chest.
He attends a Hallowe’en party thrown by the Devil – where other guests include Hitler and Diana, Princess of Wales — but is kicked out because he is not in fancy dress.
John Beyer, of TV watchdog Mediawatch, branded the cartoon unacceptable and “grossly insensitive” coming so soon after Irwin’s death in September.
But Comedy Central spokesman Tony Fox said the network had no qualms about showing the episode and would do so again.
“The South Park guys do inappropriate things, that’s what they do,” he said.
“Their goal is to make people laugh, not to offend people.
“We recognise that they do a lot of provocative things — is this one of them, probably yes.
“They are largely free to do what they like in terms of creativity and kinds of subject matter, and this is just another example of that.”
In the episode, the Devil first believes the Irwin figure at his party is someone in costume, and tells him it is not appropriate, saying: “It’s just a little soon, you know, I mean he just died a few weeks ago.”
But when the character reveals he really is Irwin he is told he must leave because he is not in fancy dress.
Mr Beyer called for the cartoon not to be shown in other countries.
“Mr Irwin’s family are obviously still grieving about their tragic loss and it seems inappropriate to me that South Park should be trying to make some capital out of it,” he said.
“To lampoon somebody’s death like that is unacceptable.”
South Park is shown on satellite by MTV and the Paramount Comedy Channel.
The expletive-littered show, caused a row earlier this year when it mocked Tom Cruise and Scientology.