The Reformed Church parishes in Baranya County under Ottoman occupation constituted a separate district from 1608 but in 1714 they were attached to the Lower Danubian Church District again; the majority of them belonged to the Upper Baranya and a minor part belonged to the Lower Baranya-Bács-Slavonia Diocese. Until the first third of the 20th century Siklós was the centre of the life of the Upper Baranya Diocese of the Reformed Church. As a result of the Trianon Peace Treaty, the majority of the churches of Baranya was ceded to Yugoslavia, so in 1952 the Baranya Diocese was formed instead of the Upper Baranya Diocese; its borders coincide with the county borders.
According to the normal practice of the administration of the dioceses of the Reformed Church, the records of the administration and management of the Baranya Diocese were collected in the deanery. For centuries diocesan archives meant portable letter boxes, which were moved to the residence of the current dean. There was an increasing demand for the safe-keeping of the documents, so in 1868 it was decided by the Siklós general assembly that the archives should be kept in a room of the vicarage in Siklós and maintained and arranged by a pastor. Later, in 1902 the general assembly of the diocese entrusted the diocesan treasurer with the maintenance of the archives. At the time the access to the records and the preparation of archival aids were not regarded as archival tasks. During the Second World War the leaders of the Upper Baranya Diocese of the Reformed Church tried to secure the records but in March 1945, during the German breakthrough the majority of the decanal records were destroyed.
In 1954 the archival material of the Baranya Diocese was permanently deposited in the Ráday Archives of the Danubian Reformed Church District. Although certain documents remained in Siklós, from this time the position of the diocesan archivist was not fulfilled and little emphasis was put on the safeguarding and arranging of the remaining records. Owing to lack of space, from 1977 the Ráday Archives could not take in more material and the congregation of Magyarbóly offered his church to store the archival material temporarily, because since the 1970s the pastor of Magyarbóly, Emil Kovács had collected a lot of material from the deserted vicarages and churches. By 1982 the collection of the archival material had been completed in the Magyarbóly church. However, ten years later construction work started in Magyarbóly; this is why the archives were moved to the vicarage in Zengővárkony in 1982. Then in September 1999 the archival material was transferred to Pécs and placed in the building of the grammar school of the College of the Reformed Church. During that year the archives were declared private archives open to the public by the Minister of the National Cultural Heritage. In the summer of 2009 the archives were relocated within the diocesan educational complex and placed in the earlier vicarage of the institution, where a special ministerial library was established as well. (After 1990 the special library acquired thousands of volumes by taking in the La Bouchere inheritance from the Netherlands and the inheritance of László Márton Pákozdy, Theology Professor from Budapest.) At last in October 2011, on the initiative of archivist Zsuzsanna Andrási Marton, almost 300 storage units were restituted by the Ráday Archives, among them several documents of great importance from the 18th and 19th centuries.
The core of the archival collection is the administrative and economic documents of the parishes, including the parish registers, the minutes of the ecclesiastical organizations’ meetings and ecclesiastical court records. The first registrations from 1747 can be found in the Okorág, Nagyharsány and Botyka marticulae. The registries were written in Hungarian. Latin and German entries can be found in protocols and parochial letters.