MLA

Diagram of the State of Illinois, Accompanying the Report of the 20th of October,1848; [by] F.R. Conway. [U.S. Dept. of Interior, General Land Office], 1848. https://collections.library.yale.edu/catalog/15814437.

APA, 6th edition

Diagram of the State of Illinois, accompanying the report of the 20th of October,1848; [by] F.R. Conway. (1848). [Maps]. [U.S. Dept. of Interior, General Land Office], https://collections.library.yale.edu/catalog/15814437.