It has never been clearly stated what city Calvin lives in, or even whether the city is an original creation of Bill Watterson's.
Certainties
Among the few certainties, we know that:
- Calvin lives in the United States.
- The town is vaguely similar in some regards to Watterson's home town of Chagrin Falls, Ohio.
- It is explicitly stated that Calvin lives neither in Florida, California, North Dakota, Arizona, Alaska, Hawaii, Montana or The Yukon.
- He lives in a state where it snows in the winter.
Speculation
In one comic Calvin becomes a giant and walks downtown (he also went there on his Flying Carpet). There, we see many skyscrapers and the area appears to be up against the ocean. The city was probably once a harbor town and could likely be Cleveland. Also, when Calvin floated away on his balloon, he mentions a river and a town triangle, and on the back of The Essential Calvin and Hobbes a giant Calvin is seen rampaging through the town triangle in Chagrin Falls, Ohio all the while holding Chagrin Falls Popcorn Shop.
In another comic, Calvin's father said that it took an hour and a half of driving to get to the beach. Because Calvin is close to downtown and lives in a rural area, he seems to live in the suburbs of a big city.
Also, during the trip back from Mars, Hobbes states that they live near the letter "E" in "[United] States", which on most maps is in Illinois, indicating they likely live in the Midwestern United States.
In one strip, Calvin had a map of Montana that he carried as part of a "Be Prepared Kit". Hobbes mentioned how "close" his state was to Yukon on a globe, however, his conception of distance is probably flawed.
It is possible that Calvin lives in Washington state, Oregon or Ohio.