Burlington County is located in the U.S. state of New Jersey. The county seat is Mount Holly. This county is part of the Delaware Valley area. Burlington County has the largest area of New Jersey's 21 counties.Burlington County has a total area of approximately 819 square miles of which 98% is land and 2% water. As of the 2000 census, there were 423,394 people, 154,371 households, and 111,610 families residing in Burlington County, NJ.