Zenith is a typical midsize Midwestern city. Lewis was very critical of the similarities between most American cities, especially when compared to the diverse—and in his view, culturally richer—cities of Europe. Frowning on the interchangeable qualities of American cities, he wrote: "it would not be possible to write a novel which would in every line be equally true to Munich and Florence." This is not true of Zenith, Babbitt's literary home. Zenith is a fictitious city in the equally fictitious Midwestern state of "Winnemac," adjacent to Ohio, Indiana, Illinois, and Michigan. (Babbitt does not mention Winnemac by name, but Lewis's subsequent novel Arrowsmith elaborates on its location.) When Babbitt was published, newspapers in Cincinnati, Duluth, Kansas City, Milwaukee, and Minneapolis each claimed that their city was the model for Zenith. Cincinnati had perhaps the strongest claim, as Lewis had lived there while researching the book. Lewis's own correspondence suggests, however, that Zenith is meant to be any Midwestern city with a population between about 200,000 and 300,000.
While conducting research for Babbitt, Lewis kept detailed journals, in which he drafted long biographies for each of his characters. For his title character this biography even included a detailed genealogy, as well as a list of Babbitt's college courses. Zenith's major names and families are documented in these journals, and many of them emerge again in Lewis's later writings. Zenith's layout is also imagined in careful detail. Lewis drew a series of 18 maps of Zenith and outlying areas, including Babbitt's house, with all its furnishings.
Zenith's chief virtue is conformity, and its religion is "boosterism." Prominent boosters in Zenith include Vergil Gunch, the coal dealer; Sidney Finkelstein, the ladies' ready-to-wear buyer for Parcher & Stein's department store; Professor Joseph K. Pumphrey, owner of the Riteway Business College and "instructor in Public Speaking, Business English, Scenario Writing, and Commercial Law"; and T. Cholmondeley "Chum" Frink, a famous poet of dubious talent. As a realtor, George Babbitt knows well the virtues of his home city. In a speech to the Zenith Real Estate Board, he states: "It may be true that New York, Chicago, and Philadelphia will continue to keep ahead of us in size. But aside from these three cities, which are notoriously so overgrown that no decent white man, nobody who loves his wife and kiddies and God's good out-o'-doors and likes to shake the hand of his neighbor in greeting would want to live in them—and let me tell you right here and now, I wouldn’t trade a high-class Zenith acreage development for the whole length and breadth of Broadway or State Street!—aside from these three, it’s evident to any one with a head for facts that Zenith is the finest example of American life and prosperity to be found anywhere." Zenith is thus presented as more than simply prosperous; it is safe and wholesome.