Despite their frankly criminal underrepresentation abroad, kotatsu are well known to anime fans. The bed/table/heater hybrids are mainstays of anime households, and generally have at least one sleepy character snuggled partway under it.
However, a survey by WeatherNews.jp found that slightly less than half of responding Japanese households have a kotatsu in them - 48% with and 52% without, to be exact. (Then again, it could just be that the people who have them were too comfy to get up and answer a survey.)
Broken down by prefecture, though, there are some places where the love for kotatsu is still strong. Yamanashi has the highest ownership rate, with 75% of households reporting owning one. Fukushima and Nagano are close behind at 72% each.
The lowest ownership rate goes to Hokkaido (23%), followed by Okinawa (30%) and Tokyo's metropolitan area (35%).
Many considered it strange that the northerly island of Hokkaido would have not only a lower ownership rate than the southern island of Okinawa (where the temperature rarely dips below 70F), but the lowest rate of Japan as a whole. But there's a good reason -- most houses on the island, where the temperature is often below freezing from December to March, are equipped with central heating. So kotatsu and space heaters are less necessary.
Kara Dennison is responsible for multiple webcomics, blogs and runs interviews for (Re)Generation Who and PotterVerse, and is half the creative team behind the OEL light novel series Owl's Flower. She blogs at karadennison.com and tweets @RubyCosmos. Her latest story can be found in My American Nightmare.