A few months back, I posted some data from a federal reserve website that had 60-90 day lates. It was a pretty good tool, you could break it down by country for every state. It had those delinquencies at like 9% for prime. Then from another article I found data regarding the subprime and Alta-A delinquencies which was like 15% and 23% respectively. However that was for all, including 30 days. So for SD country that may not be far off.
Doing a quick back of the envelope given 600K thousand mortgages in SD and how they break down per mortgage type you can get some rough numbers regarding people not paying. Which probably is not to far off from 15-16%.