Legal Question in Family Law in California

Yes, you would still be responsible unless the county released you. The other parent has no ability to forgive that debt. For further information, visit http://www.ellifritzlaw.com

If you are the adopting step-parent, no.

Both answers are correct. You fail to specify whether you are the adopting step parent or the bio parent. The bio parent's unpaid liability, whether to the state or the other parent, for child support payments and reimbursements does not go away if and when a step parent adopts the child. The liabilities stop accruing, but they do not go away. Likewise, the adopting step parent does not become liable for back support or reimbursement, but could become liable in the future in circumstances that any parent might become liable for such payments going forward i.e., divorce or legal separation.