what county is hopatcong, nj?
Homefacts City Report. Hopatcong is located in Sussex County, NJ. The population is 15,169, making Hopatcong the largest city in Sussex County. There are 6 public schools in Hopatcong with an average Homefacts rating of C. The total crime rate for Hopatcong is very low, and there are 7 registered sex offenders residing in the city.