I did not know where my son's father had relocated. However I know have his home address. My son is an adult now is the father still liable to pay child support?

What age is your son?

Is there a child support order in place? If not, you cannot file after the age of majority.

If the child is now a adult, and you never had a child support order in place from the court, you can not apply for one now, it is too late.

If you had a court order for child support and they owed you support that was not paid, depending on the number of years, you may go back for collection of some of that.

If you waited until now with no court order for child support, it's basically too late to do anything about it. Sorry.

Plus the "adult" should be getting a job. Is this adult disabled? If so, you need to look into getting disability benefits for this adult.