St. Mary Cathedral is a cathedral of the Roman Catholic Church in Lansing, Michigan one block north of the Michigan State Capitol. It is the seat of the bishop of the Roman Catholic Diocese of Lansing.

The Diocese of Lansing is a Latin Church ecclesiastical territory – or diocese – of the Catholic Church located in the south-central portion of Michigan in the United States. It is a suffragan diocese in the ecclesiastical province of metropolitan Archdiocese of Detroit.