Actually it was not always clear that Clark Kent was raised in Kansas. In one map of Sueprman/Batman world, they show Metropolis and Gotham City on the Delaware Bay, and Smallville as essentially a Suburb of Metropolis. They actually have the map at the Smallville (comics) article on wikipedia.
There was a 1978 publication that said that Smallville was a quiet town nestled in the hills just inland from the Eastern Seaboard.
"The Adventures of Superman" Radio show had Clark raised on the farm of Eben Clark in Iowa, this was in the 1940s. A 1984 comic publication placed Smallville in North-east Pennsylvania or Northern New Jersey.
It is only with John Byrne's Superman reboot in 1986 that Smallville comes to be universally designated as in Kansas.
