St. Ambrose Parish in Garrettsville in northeast Portage County goes back to a mission established in 1885 by Father Ambrose Weber, pastor of St. Mary Parish in Warren, who pursued missionary work in Trumbull and Portage counties—traveling by bicycle, handcar, or freight train to celebrate Mass in Garrettsville. Though the mission was closed in 1901, the advent of World War II led to establishment of the Ravenna Arsenal in the Windham-Ravenna area, drawing more workers. In response to requests, Cleveland Archbishop Joseph Schrembs assigned a pastor to reopen the mission. Those Masses were held in 1942 in the Garrettsville Opera House.

Meanwhile, the Village of Windham, seven miles east of Garrettsville, grew from a few hundred to approximately 5,000 by the mid-1940s. So, Catholics in Windham petitioned Bishop James McFadden, who assigned a pastor to serve Catholics in Windham as a mission of Immaculate Conception in Ravenna. The St. Ambrose Mission officially became a parish on February 4, 1944, and soon, St. Ambrose was given responsibility for the St. Michael Mission.

Description from The March of the Eucharist, 2nd edition (2025) published by The Catholic Echo