The land that Mack was residing on was originally claimed by Joseph Thiebeau who bought the rights for a section of land for his daughter under the terms of a treaty signed at Prairie du Chien on August 1, 1829. Subsequently the daughter died young making Joseph the legal heir and owner of the section, and on January 17, 1838 Thiebeau sold the land to Jean Baptiste Beaubien, a well-known trader active in Chicago for many years. By June 1838 Beaubien was a partner with Stephen Mack, and, along with John P. Bradstreet, began selling lots in the new community.