I can't find a reference on the Guiness World Records web site, but this news article from 2010 says:
> And if you were wondering, according to the Guinness Book of World Records, The World’s Longest Yard Sale” runs along a 630-mile stretch of U.S. Highway 127 from Gadsden, Ala. to Covington, Ky.
Here is some more evidence pointing to the Guiness World Record in 2004:
> Contrary to the hopes of some participants, this sale won't even come close to breaking the Guinness World Record for longest yard sale.
>
> "No, no," Weiler said. "There's a 450-mile yard sale on Highway 27 that runs through four states in the South - that's where I got the idea for this one."