The novel's secondary protagonist, the practical and content Kennicott provides a foil to his imaginative and restless wife. While Carol longs to bring beauty and culture to Gopher Prairie and create social reforms, Will remains comfortable with his hometown as it is. While she is romantic and interested in the fine arts, he is realistic and materialistic. Although he is intelligent and insightful, he does not appreciate poetry or drama as his wife does, preferring cowboy movies to the theater. Throughout the novel, Dr. Kennicott fails to understand his wife's dissatisfaction with the town, instead absorbing himself in his profession and in small practical duties such as fixing his furnace or investing in land. The literary critic H.L. Mencken wrote, "To Will Kennicott as to most other normal American males, life remains simple—do your work, care for your family, buy your Liberty Bonds, root for your home team, help to build up your lodge, venerate your flag." While Carol finds the people of Gopher Prairie unimaginative and unsophisticated, Will considers them kind and friendly. He himself is dull but also friendly and easygoing. In all, he remains a stable, reliable, and unexciting character throughout the novel. While Carol's character matures by the end of the novel, Kennicott's character remains the same.
Although Will is rather dull compared to his wife, he is also a heroic doctor who can handle emergencies with calm and competence. In Chapter 15, Lewis describes Kennicott's profession in detail and, like Carol, expresses admiration for his professionalism and dignity. Lewis himself admitted that Kennicott's prototype was his father, Dr. E.J. Lewis. Some critics have remarked that Lewis' conflicting portraits of Kennicott—one presenting Kennicott as a dull, unimaginative boor and the other presenting him as a hero—reflect the author's own mixed feelings of antipathy and admiration toward his strict physician father. However, Lewis maintained that he intended the portrait to be complimentary.
The Kennicott's marriage proves to be a major theme in the novel. Lewis presents their marriage realistically rather than idealistically, reflecting the modern stresses of marriage. As Kennicott continually fails to understand his wife's dissatisfaction with Gopher Prairie, their marriage continues to deteriorate. However, Will never ceases to believe that his wife will come to love and accept the town as it is. He has an unswerving affection for Carol, tolerating her ideas and activities— such as her friendships with the Bjornstams and with Erik—while gently condemning them at the same time.
In many ways, the conservative Kennicott represents Gopher Prairie itself. He resists change and shares Gopher Prairie's practical and materialistic personality. The final scene of Main Street, in which Will and Carol talk, encapsulates much of the nature of their contrasting personalities. While the dreamy Carol imagines future social reforms she might engender, the practical Kennicott thinks only about the weather and his storm windows.