The animator, who is 55, issued a statement that he will keep working on the series as long as he can.
"I wanted people to hear directly from me that I have been diagnosed with ALS.," the statement reads. "Anyone who knows me knows that I will continue to work on 'SpongeBob SquarePants' and my other passions for as long as I am able. My family and I are grateful for the outpouring of love and support. We ask that our sincere request for privacy be honored during this time."
Nickeleoden, the network that has aired "SpongeBob" since 1999, said in a statement: "Steve Hillenburg is a brilliant creator who brings joy to millions of fans. Our thoughts and support are with Steve and his family during this difficult time. Out of respect for their wishes for privacy, we will have no further comment."
A source close to Hillenburg says that the animator is in the early stages of the disease and was only recently diagnosed.
ALS (amyotrophic lateral sclerosis) affects nerve cells in the brain and the spinal cord, leading to paralysis. Astrophysicist Stephen Hawking, who was first diagnosed in the '60s, also suffers from a slow-progressing form of the disease. It was originally called "Lou Gehrig's disease," after the baseball player who was first diagnosed with it in 1939.
Hillenburg is a former marine biology teacher who drew on his love of the ocean to create the goodnatured yellow guy "who lives in a pineapple under the sea." He directed 2004's "The SpongeBob SquarePants Movie," and co-wrote and produced the 2015 sequel.
Last year Nickelodeon renewed "SpongeBob" for its 10 and 11th seasons.