Here's a quote from the book that confirms this:
> "Dill Harris, a thin, gangling boy with a shock of pale hair and a perpetual grin, lived in Meridian, Mississippi, during the school year, but every summer he came to Maycomb to spend his holidays with his aunt, Miss Rachel Haverford, who lived next door."
>
> - Chapter 1, To Kill a Mockingbird
This quote clearly states that Dill's permanent residence is Meridian, Mississippi, and he only spends his summers in Maycomb.