If you check out the HANDYBOOK, which is a genealogical goldmine for all researchers you will soon discover that not only was Warren county once a part of Sussex County, but it was also part of Morris County and before that Hunterdon county. The original county was Burlington. By checking this source/resource, you will learn the time line for the breakout of each. Warren wasn't formed until 1824, so anyone with people in New Jersey and in that area needs to find out the date when each county was formed. This book should be included among every genealogists personal library along with others. It doesn't matter which volume you get, current or an older one, the dates aren't going to change from edition to edition, just some other info might be included or retracted in subsequent issues. I believe it might be up to the 9th or 10th edition, but if you have earlier ones, they work just as well for New Jersey research. Your local public library should also have a copy in their reference section. If you can't afford a personal copy, go to the public library and copy out the information for your particular states of interest and put the copy into a binder or file folder for future reference when researching. Also, keep in mind that the first census you can lay your hands on is the 1830 for any county of research in New Jersey. All those before that time have been destroyed and do not exist. This makes doing research in New Jersey a challenge! Christie Trapp