How can I help my grown mentally ill son who is not inclined to hurt himself or anybody else. Just doesn't want any help.

I am so sorry for your situation; you have my deepest sympathy.   You can't force your son to get help, or to accept it. You can take steps to ensure that you do not leave him any assets outright. You can also take steps to ensure that any assets that you do leave him will be available and can be used by a third party in ways that will help him and not allow him to indulge in self-destructive behavior with your assets. You should consider having your estate planning provide for your son's share of any inheritance you may leave him pass to a trust for his benefit- either a full-blown supplemental needs trust (a "third-party" one, since it will be funded by you, with your assets) or a community pooled trust. That way, if he is ever eligible for and applies for needs-tested benefits like Supplemental Security Income and Medicaid, the trust won't count against him, but it can be used to help improve his quality of life as much as possible, and he can't just waste it. That way, it will be there for him if and when he is ready to seek help, and it will be there for someone to use to help him as much as possible even if he continues not to seek help.   Find an attorney who works with familiies with disabled family members on estate planning matters, and get an estate planning consultation. Best wishes to you.