Hey, I remember a similar analysis of this back in 2009. https://web.archive.org/web/20090925222851/http://www.weathe... , with HN comments at https://news.ycombinator.com/item?id=840542 .

That one determined: "Between the tiny Dakotan hamlets of Meadow and Glad Valley lies the McFarthest Spot: 107 miles distant from the nearest McDonald’s, as the crow flies, and 145 miles by car!"

That was done with "13,000-or-so U.S. restaurants", this new one with "almost 14000 locations".