Mont. Code Ann. § 52-2-612

If a child has been placed in substitute care, as defined in 41-5-103 and 52-2-602, and a written agreement for payment of support has been entered into by the responsible parent or parents and the department, the debt for support is limited to the amount provided for in the agreement. However, if a court order for support is or has been entered, the order prevails over the agreement.