Madison is a city in and the county seat of Jefferson County, Indiana, United States, along the Ohio River. Its estimated population was 12,083 as of 2012. Over 55,000 people live within 15 miles of downtown Madison. Madison is the largest city along the Ohio River between Louisville, Kentucky and Cincinnati, Ohio. 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.