Jinx the cat from the cartoon Pixie and Dixie.
You might be able to count the Jailbird (early name of Snake) on The Simpsons. Also, the old guy Jasper.
Johnny Bravo
Jonny Quest
Johnny Test
Jerry (Tom and Jerry)
Josie (Josie and the Pussycats)
Joey Wheeler (Yu-Gi-Oh)
Jimmy Neutron
Jake Long (American Dragon)
johnny bravo.
The Joker?Juggernaut (X-men)
Jerry, from Tom and Jerry
Judy Jetson the jetsons the jetsons
Jade or Jackie Chan from Jackie Chan Adventures.
Jerry as in Tom and Jerry.
No there is no Mario character that starts with a J
Jerry, the mouse in TOM & JERRY.
Frostbite Falls, MN
Jonny test
jimmy neutron
Jerry, from tom and jerry