1926 - Archbishop Messmer establishes Diocesan High School (now Messmer High School) with 166 students.
1928 - Diocesan High School renamed Messmer High School after Archbishop Sebastian Gebhard Messmer.
1940 - Enrollment reaches all-time high with two shifts of classes to accommodate more than 1,400 students and no freshman classes.
1980 - Messmer begins to see a steady decline in student enrollment.
1984 - Archdiocese of Milwaukee announces the closure of Messmer High School and Save Messmer Committee is formed.
1984 - With support from the DeRance Foundation, the Messmer school building is purchased from the Archdiocese of Milwaukee.
1985 - Messmer High School reopens with 115 students and 16 faculty members and becomes the first independent Catholic school in Milwaukee.
1995 - Messmer High School becomes the first religious school accepted into School Choice program.
1998 - Archbishop officially recognizes Messmer as an independent Catholic school.
1999 - Messmer Catholic Schools is established to oversee Messmer High School and the new Messmer Preparatory Catholic School (formerly St. Mary Czestochowa).
2007 - Messmer Catholic Schools assumes management of St. Rose and St. Leo schools at the request of the Archdiocese of Milwaukee.