The traditional answer is
Tandy Leather Factory.
There is also
Brettuns Village.
And there is usually a local (at least in the same state) leather store. Most states have a physical Tandy store. But there are often other stores, for example, in Washington I normally frequent
MacPherson Leather.
From a quick Google search, looks like there is a
Weaver Leather Supply about an hour south of you, and a Tandy about 45 minutes north (if you want in-person, as opposed to online).