Question: Bio father signed over rights, but still owes over 25,000 in back child support. Am I able to go after him for the unpaid child support? I know that since he was adopted by my husband he is no longer responsible, my question is all the back support from years ago?

Where is this at, and how many years ago.

Normally yes they owe it, but how many years did you wait to attempt to collect

This is Indiana, he was ordered 8 years ago and hasn't paid in 6 years. We just recently found him to sign off rights, he fell off the radar. It may sound petty to be going after the money, but I feel it's my sons money and I can put it away for him.

Depending on the state law even though he signed over right he may still be responsible for paying child support still! Other then that most states and counties have their own child support inforcement agencies you can contact to ask these questions.

he may still be responsible for paying child support still!

This is incorrect. The child was adopted by the step father. That ended any ongoing support obligation.

However, he does continue to owe any arrears that have not been paid. And yes, you can continue to pursue that through the courts and/or the Indiana child support collection agency.