In virtually every facility we are aware of, personal checks are not accepted for inmate accounts. The reasons are practical ones. Personal checks can bounce, can be fraudulent, and create administrative headaches that understaffed mailrooms and finance offices are not equipped to handle. Facilities moved away from accepting them years ago as electronic payment options became available.
The good news is that putting money on an inmate's books is easier now than it has ever been, and there are several reliable options depending on the facility.
Most jails and prisons use a third-party platform for deposits, with JPay, Access Securepak, TouchPay, and ConnectNetwork being among the most common. You can deposit funds through those platforms online, through their mobile apps, or at kiosk locations in some areas. The facility's website or a quick call to the jail will tell you which service they use and what the deposit options and fees look like.
If you previously made a deposit online and cannot find where you did it, try checking your email for a confirmation receipt from the original transaction. That will tell you which platform you used. If that is not available, searching the facility name along with the word deposits or commissary will usually surface the right platform quickly.
InmateAid can also point you in the right direction if you reach out to aid@inmateaid.com with the facility name and location.