It came to my attention a few years ago that there is an online community of people who "collect counties," attempting to visit as many of them as possible – sometimes all 3142 in the U.S. "I could be one of them," I thought, and proceeded to do many hours of research to determine which ones I had already visited. This was a not insubstantial total, as I'd been on three cross-country road trips with my family when I was younger, in addition to sundry and varied drives between New England, Virginia, Minnesota, and/or Oregon, all which regions I've lived or attended school in.
My tally now stands at 1357 counties that I'm sure I've visited, or 43.2% of the U.S.'s total. I am now at the point where I intentionally take spur side trips to spend two minutes tagging the corners of very remote counties that I doubt I'll ever actually pass through on my way to something (Owyhee in Idaho or Wabasha in Minnesota being recent examples). They all count. Airports do not (for me). Trains, cars, and foot travel do. My map at mob-rule.com differentiates between mode of travel when I most recently visited each county. I am proud to say that I have literally only walked through some counties (the green ones on the map).
My interest in long drives is definitely hereditary, as I have a grandfather whose county tally would have numbered, conservatively, in the bajillions if he had bothered to keep track over his quite remarkable life. He never flew anywhere, period – while I do, grudgingly, if it's unavoidable due to time constraints – and his method of moving or helping family move around the country was to make as many runs as needed with possessions piled into the back of his pickup truck. I fully intend to continue that legacy.