St. Mark School is accredited by the State of Illinois, the Diocese of Peoria, and the North Central Association/AdvancEd.

St. Mark School has earned continuing accreditation from the North Central Association Commission on Accreditation and School Improvement (NCA CASI), an accreditation division of AdvancED.

NCA CASI provides nationally-recognized accreditation, the purpose of which is continuous school improvement focused on increasing student performance. To earn accreditation, schools must meet NCA CASI's high standards, be evaluated by a team of professionals from outside the school, and implement a continuous process of school improvement. Accreditation is granted on a five-year term.