My boyfriends son is 18. He has paranoid schizophrenia
And receives $698 monthly in SSI benefits. He is on a waiting list for an apartment that will cost him $120 per month, approx. $80 per month in utilities as well as receive $200 mth in food stamps. He divorced his xwife 3 years ago, prior to the illness. In the divorce he was req'd to pay child support for his son. Now that he will be living on his own and will have over $500 per month after living expenses, can the sate of Indiana order that he continue to pay child support to his son or to the state? His xwife is also trying to get his son declared incapacitated but his case worker says he is absolutely not disabled and they are hoping he will flourish on his own, possibly taking college courses and getting a part time job.

You make it sound like the son got married at 15 and divorced at 18 - I assume you mean your boyfriend.
Your boyfriend will have to apply to the court for a change in payments. He needs to look at the exact wording of the divorce agreement too, which should specify what happens when the son turns 18.
We can't know if he is 'incapacitated' or not, but I wouldn't worry about it, because he is being given an apartment, a sign that he is considered to be OK living on his own, with support. There's a huge difference between incapacitated and disabled. Disabled has a wide range of abilities, even within the group of people with paranoid schizophrenia. Some will be reclusive and/or in and out of hospitals, others will indeed get jobs and go to school. Some will vary over the years. Fighting over that just because of money is unfair to him.