MDOC's 15 college credit rule, in plain words
To work as a Michigan Department of Corrections officer you need 15 semester credits, or 23 term credits, of college coursework. MDOC's current page says they can be in any academic or degree-prerequisite area. You can be hired without them if you agree to earn them within 24 months, but finishing inside that window is required to stay employed.
The rule rests on the Correctional Officers' Training Act of 1982. MCL 791.512 sets 15 semester or 23 term credit hours of coursework from an accredited postsecondary institution, or a relevant degree, as part of certification, along with an internship and new employee training. Older job postings listed set subjects such as criminal justice, psychology and sociology, or a shorter window; follow MDOC's current page and ask HR if a posting differs.