Oddly, the biggest of the towns I've looked up so far (I'm through Maine) is in my home state of Arizona -- I figured I knew most of the decent-sized towns there, so if I picked one I'd never heard of, it would surely be a real flat patch in the road. Put Paulden, AZ, is a thriving metropolis of just over 3000 people -- practically New York by the standards of this experiment. Other unexpectedly large towns: Fort Deposit, AL (pop. 1270), Cornwall Bridge, CT (pop. 1300), and Union Point, GA (pop. 1669). Not so large: Platina, CA (pop. 206), Gulf Hammock, FL (pop. 254), and Ricketts, IA, whose population of 141 is less than that of the factory where I work on a given weekday.
The biggest hassle, other than the asinine possibility of actually going to all these places, has been where I've picked out a place that either does not exist (as with Merrimac, KY, which is listed in my atlas, but to which I have been unable to find any reference anywhere else -- it may be one of those fake places that cartographers put on maps to protect their copyrights), or that does exist but may be a geographical feature rather than a town (as with Lowes Crossroads, DE), or that exists and is a town but which I am unable to find any population data for (as wtih Hoolehua, HI), or exists and was a town at one point but may no longer be one (the only population figure I could find for Warm Lake, ID was from 1960; it listed the population as eight, and it didn't really seem like a boom town), or that was a town at one point but now just seems to be an abandoned ranch (as with Powder Wash, CO).
More on this completely idiotic project as it develops.