The Mennonite Historical Society of Ontario is a group of people who work together to encourage and support projects that interpret Mennonite heritage to Mennonites and non-Mennonites.

These projects include:

Publications: Publication of a twice-yearly newsletter called Ontario Mennonite History. Between 1983 and 1992 it was called Mennogesprach. This newsletter includes all types of historical articles and book reviews as well as news about what is happening with the historical society. The periodical is received by all members of the society.

Public Meetings: Meetings in the spring and the fall involve speakers and sometimes bus tours about a variety of historical topics. Recent topics have included Mennonites and the War of 1812, and Mennonite and black settlers in the Queen's Bush.

Historic Sites:  The Mennonite Historical Society of Ontario supports two historic sites. The Brubacher House is a restored 1850 Mennonite farmhouse on the University of Waterloo campus on Columbia Street west. The Detweiler Meetinghouse is a restored 1855 stone Mennonite meetinghouse near Roseville.

Books and resources:  Through the J. Winfield Fretz Publication Fund, the Mennonite Historical Society of Ontario supports the publication of books and other media projects that provide information about Ontario Mennonite heritage.

The Mennonite Historical Society of Ontario is affiliated with Conrad Grebel University College, the Mennonite Archives of Ontario, and the Mennonite Historical Society of Canada.