When my son was born I let my mother-in-law and her husband adopt him. I signed my parental rights over to them, but half way through the adoption they got a divorce and never finished the adoption. Now the state is coming after me for child support. What are my rights.

Your rights are those of any father. You can pay child support and if you choose, you can request visitation and perhaps custody through the court.

What I suspect happened was that you signed the papers to terminate parental rights but they were never filed with the court. You could call the court to verify this.