New Castle is a city in Henry County, Indiana, 44 miles (71 km) east of Indianapolis, on the Big Blue River. In 1900, 3,406 people lived in the town; in 1910, 9,446; in 1920, 14,458; and in 1940, 16,620. The population was 17,780 in 2000. The city is the county seat of Henry County. New Castle is home to New Castle Fieldhouse, the largest high school in the world.