Born Richard Wayne Van Dyke on Dec. 13, 1925 in West Plains, MO, he was raised in Danville, IL - the same hometown as his later "Van Dyke Show" character, Rob Petrie - by his parents Hazel and Loren "Cookie" Van Dyke; the latter, a traveling salesman with a knack for making customers laugh. Van Dyke attended high school in Danville (among his friends at the time were actor Gene Hackman and nightclub legend Bobby Short) and was a fixture in local theater productions.
Danville seems to be the accepted answer, however:
26. The sitcom is inconsistent on the point of Rob's hometown. In one episode, an old high school girlfriend from Danville shows up looking for an audition with Alan Brady. In another episode, Rob's parents come from Danville to visit. But in yet another episode, a male school friend (played by Jack Carter) appears and the two reminisce about their childhood in Westville, which seems like a composite of West Plains, Missouri (where Van Dyke grew up), and Danville, Illinois (where he moved as a young man to seek his fortune).
On the show, Rob and Laura lived in New Rochelle, a suburb of NYC where Rob worked as the headwriter for a TV series. This is based on Carl Reiner's autobiographical information.
The 1961-1966 TV hit The Dick Van Dyke Show starring Dick Van Dyke and Mary Tyler Moore as Rob and Laura Petrie. The Petrie family lived on 148 Bonnie Meadow Road (a fictional address) in the North-end of the city.
^ The Dick Van Dyke Show, By Ginny Weissman, Coyne Steven Sanders, 1993, page 2
As with Enter Laughing, Reiner's sitcom was autobiographical. Like Petrie, Reiner was a New York writer who lived in New Rochelle.