New Jersey now has 13 counties that rank in the top 150 hottest real estate markets in the U.S., according to the latest data from Realtor.com for January. That’s up from nine counties that made Realtor’s home sales hotness rankings in December. Somerset County, where the median listing price was $609,500, was the highest ranked New Jersey county on the national list at 18. Eleven New Jersey counties ranked in the top 100. Monroe County in New York and Hillsborough County in New Hampshire had the hottest markets in the U.S. Realtor.com calculates its hotness rank based supply and demand data o…