The key question is whether his state DOC inmate number has been assigned yet. Once a person is sentenced to state prison, they are typically assigned a DOC number even before the physical transfer happens. If he has that number, you can deposit money directly into his state DOC account through the state's official deposit platform, and those funds will be waiting for him when he arrives at his assigned facility.
To find the right deposit method, go to the Department of Corrections website for his state and look for the inmate account deposit or commissary link. Most state systems use a platform like JPay, Access Corrections, or a state-specific service. You will need his full legal name and DOC number to complete the deposit.
If he has not yet been assigned a DOC number, you can still put money on his county jail account, but those funds may or may not transfer automatically to his state account when he moves. County and state systems are separate, and the process for transferring remaining balances varies by jurisdiction. The safest approach is to confirm his DOC number first and deposit directly into the state account.
InmateAid can help you identify the right deposit method once you know which state facility he is heading to.