Jacobo Sedelmayr, born in Freising, Bavaria in 1703, was a Jesuit missionary. He was sent to New Spain in 1736 and was assigned to the Pimeria Alta region, which includes what is now Arizona. In 1751, eight missions were active in Pimeria Alta. Sedelmayr was Visitador Provincial, located at Tubutama. Also that year, a revolt of the Pimas created a major setback for the Jesuits. Sometime between 1754 and 1762, Sedelmayr was transferred to the mission of Tecoripa, in the province of Sonora. In 1764, he became professor at the College of Matape on the Yaqui River. On June 25, 1767, the Jesuits were expelled from Mexico. Sedelmayr found refuge in Spain and died at Aldea de Avila, Spain on February 12, 1779.
Letters and reports, from Sedelmayr to various Jesuit leaders, describe conditions in Pimeria Alta at the missions and surrounding areas, discuss administrative concerns, and report on explorations along the Gila and Colorado Rivers.
The documents provide a detailed account of the land and people he encountered including Pima, Tohono O'odham, Apache, Yuman, and Seri. They also contain information on the organization and operations of the Jesuit missions in the Pimeria Alta. Correspondents are Christobal de Escobar y Llamas, Juan Antonio Balthassar, Philipp Segesser, and Andres Xavier Garcia.
Three letters and one report are contemporary holograph documents. Seven letters and two reports are photocopies of holograph documents. All are in Spanish, with some lapses into German interspersed; and are accompanied by typescript English translations or summaries.