Where the Outhouses Are

Wonkblog:

Who doesn't have a flushing toilet?
As it turns out, a lot of people. According to the latest American Community Survey, nearly 630,000 occupied households lack complete plumbing facilities, which means that they are without one or more of the following: a toilet, a tub or shower, or running water. The Census Bureau says that the average household contains 2.6 individuals, which means that today, in 2014, in the wealthiest nation on Earth, upwards of 1.6 million people are living without full indoor plumbing.
As the map below shows, there is considerable geographic variation. Counties containing Indian reservations have astonishingly high percentages of households without plumbing -- 14 percent of households in Shannon County, S.D., don't have full plumbing. In Apache County, Ariz., the rate is more than 17 percent. Sparsely-populated census areas in Alaska also have very high percentages.
Counties along the Rio Grande in Texas have high rates of unplumbed households, as do a smattering of counties in Appalachia, particularly in eastern Kentucky and western Virginia. The southwestern portion of Alabama is another hot spot.
Looking beyond the present day, it's worth remembering that indoor plumbing is a fairly new development for many communities. In 1950 fully one quarter of U.S. households did not have a flush toilet -- this means that the era of outhouses is well within living memory for many Americans. The town I live in, Oella, Md., was reliant on outhouses until 1984. And it's smack in the middle of the Acela corridor, between Baltimore and Washington.

I would guess Indian reservations and Amish counties like Lancaster, PA, Holmes, OH and Elkhart, IN.  It looks like a lot of the rest, like in Maine, Wisconsin and Minnesota might be in cabins or summer cottages which aren't used year-round.  Also, in the middle of nowhere.  Another note, this is one of the Census questions that most pisses off conservatives.  God bless the Census Bureau.