There is some debate over whether or not the town is called Granville or Grandville. The town does not appear to exist in the DC Comics continuity. In Subterranean, a bus is clearly marked "Granville". The closed captions in both Subterranean and Lexmas both said Granville, although there are reports that closed caption in another episode did once say Grandville.  Since the "d" in Grandville has never been enunciated clearly on the show and given the repeated references to Granville in the props and closed captions, it is most likely that the town is named Granville.
Another reason why the spelling of this particular city is most likely "Granville" is because of the city of Vancouver, where Smallville is filmed. Granville was the former name of the city of Vancouver. There are at least three streets in the Greater Vancouver Area which bear the name "Granville", particularly Granville Street, a major arterial in the Downtown area. There is also Granville Island, a tourist attraction on the under the south end of the Granville Street bridge across from Downtown Vancouver's peninsula. Thus, it can be argued that the name of the town of Granville in Lowell County is a homage to the city of Vancouver.