Correspondence is the largest series in the collection. Arranged chronologically, the series includes interchanges between Lorch and his university and professional colleagues. This series also includes items other than correspondence, such as reports, memoranda, and speeches. Because Lorch was in Chicago at the turn-of-the-century, he came to know Louis Sullivan and other members of the "Chicago School" of architecture. Within his collection, there is correspondence with W. M. R. French, director of the Chicago Art Institute as well as some letters from Sullivan himself. More important is Lorch's lifelong correspondence spanning forty years with George Elmslie, intimate associate and colleague of Sullivan and Frank Lloyd Wright, and Lorch's brother-in-law. As Lorch was also a student at M.I.T. and Harvard, Lorch knew and came to correspond with Denman Ross, F.W. Chandler and Warren H. Langford. Lorch's correspondence covers a range of topics, not just matters relating to architecture. For example, there is much lore and information about early 20th century academia, some documentation of the effect of the Great Depression on a vulnerable profession - architecture, the effects of World War I and II on the academic community (especially young people), and official state and professional attempts to save a visible and concrete past via architecture.
Appended to this finding aid is a selective listing of correspondents and subjects documented in the collection. This listing was prepared soon after the collection came to the library in 1965.