Madison is a city in and the county seat of Jefferson County, Indiana, United States, along the Ohio River. As of the 2010 United States Census its population was 11,967. Over 55,000 people live within 15 miles (24 km) of downtown Madison. Madison is the largest city along the Ohio River between Louisville and Cincinnati. Madison is one of the core cities of the Louisville-Elizabethtown-Madison metroplex, an area with a population of approximately 1.5 million. In 2006, the majority of Madison's downtown area was designated the largest contiguous National Historic Landmark in the United States—133 blocks of the downtown area is known as the Madison Historic Landmark District.