After the separation from the original parish of Attendorn, around 900, St. John's Chapel is not only the center of a flourishing village, but also of a parish that extends over the southern half of what is now the district of Olpe, as does the Olpe deanery, which was founded in 1923. The old patronage of St. John was only replaced around 1700 by that of St. Martin, who was venerated as the local saint. Since then, his "coat of arms" has had its place in the church seal as well as in the town coat of arms.
The parish church was badly damaged in the town fire of 1795. On July 23, 1907, on the feast of the diocesan patron saint St. Liborius, the foundation stone for the new church is ceremoniously laid. On June 10, 1909, the Corpus Christi procession moves into the new church. The people of Olpe are proud of their new St. Martin's Church, which is one of the largest and most beautiful in the Sauerland. In 1922, the new bronze bells Martinus, Agatha and Rochus are consecrated.
On March 28, 1945, 72 British bombers with over 30 accompanying fighter bombers are deployed to destroy railroad lines in Olpe. 43 bombers attack Olpe with five carpet bombing raids, killing more than 200 people. St. Martin's Church is so badly damaged that the south-western church tower has to be blown up. The approximately 35 meter high tower was never rebuilt. Today, the ruins of the tower are seen as a memorial for peace.
In 2013, an adoration chapel for Maria Theresia Bonzel, the founder of the Olpe order who was beatified in the same year, was set up in the south-west tower, which was partially blown up in 1945. Her mortal remains were transferred from the previous burial chapel at the motherhouse of the order to the parish church on November 12, 2013. The windows above this chapel are worth seeing: they are the only original windows. They had not yet been installed at the time of the bombing of Olpe, meaning that only the temporary windows were destroyed when the church was hit. As a result, the undamaged original windows were installed here after the reconstruction, while all the other church windows are new ones from the post-war period.
Source: http://www.pv-olpe.de/10923-Gemeinden/10689-Pfarrei-St.-Martinus-Olpe/74061,Die-St.-Martinus-Kirche-in-57462-Olpe.html, as at: 24.2.2017 and https://de.wikipedia.org/wiki/St.-Martinus-Kirche_(Olpe), as at: 24.11.2017