Seventy-seven inmates at the California Men's Colony (CMC) are now confirmed to have COVID-19.
The new numbers Wednesday are up 30 from Tuesday night.
Staff cases remain unchanged at seven active cases.
Testing at the state prison has increased following the recent outbreak.
CMC says it has secured a vendor for mandatory staff testing at CMC and other state prisons "to help reduce the burden on county resources."
CMC officials add that inmate movement at the facility has been restricted.