The Business and Labor collection includes a letter from Frederick Rapp to Joseph Attwood of Elizabethtown, Pennsylvania, about Attwood's business affairs (July 24, 1819).
The William Young papers contain a letter from Frederick Rapp to William Young (July 27, 1823).
Williams, A. The Harmony Society at Economy, Penn'a., Founded by George Rapp, A.D. 1805: With an Appendix. Pittsburgh: Printed by W.S. Haven, Cor. Wood and Third sts., 1866.
The William Henry Smith Memorial Library of the Indiana Historical Society has a collection of Frederick Rapp papers. The Pennsylvania Historical and Museum Commission and Pennsylvania State University have collections of material related to the Harmony Society.