With the fifth-largest population increase among all U.S. cities for the year ending July 1, 2012, Austin leapfrogged past Indianapolis and Jacksonville, Fla., to become the nation’s 11th-most populous city, according to population estimates released Thursday by the Census Bureau. Between 2011 and 2012, Austin’s population increased by 25,395, or an average of about 70 people a day. The Census Bureau estimated Austin’s 2012 population at 842,592.