Atlantic County is a county located in the U.S. state of New Jersey. As of the 2010 United States Census, the county had a population of 274,549, having increased by 21,997 from the 252,552 counted at the 2000 Census (+8.7%, tied for third-fastest in the state), retaining its position as the 15th-most populous county in the state. Its county seat is Mays Landing.