The first census in 1790 and the subsequent ones, every ten years only listed the head of household so if there were common surnames it is difficult to determine the parents in many cases.
I met John Fulford recently who has lived in Bradenton, Florida for many years, near my Fulford relatives. Since his name was Fulford he wondered if he was related to them. He was born in Virginia and as far as he had known his family had been there for a long time. All of my Fulford relatives were from Beaufort in Carteret County North Carolina.
I started to look at his family records and noticed his last known ancestor, Elijah Fulford, listed Beauford, North Carolina as his place of birth. It made me suspect he was part of the Carteret County family but I had no proof and John had no information about his ancestors before Elijah. I knew of a Fulford family in Carteret County that had a son named Elijah who was born around the end of the 1700s but the last record of him was his father's will dated 1801. The will listed his mother's name was Sarah. The Elijah Fulford in Virginia first showed up there on the 1850 census.
Then as I looked at census records, I found an Elijah Fulford listed on the 1830 census for Currituck County North Carolina. Living nearby was a Sarah Fulford who's age matched the Sarah listed in the 1801 will. Between them was a Rodney Fulford. When I went back and read the will again, I saw Elijah had a brother by that name. All of the ages matched the ages in the will. As such, I am certain this is the same family and they came from Carteret County. According to my genealogy software, John and I are 6th cousins. He now has a whole town full of relatives living around him.