Monroe County is a county in the U.S. state of Indiana. In 1910 the US Census Bureau calculated the nation's mean population center to lie in Monroe County. The population was 139,718 at the 2020 United States Census. The county seat is Bloomington. Monroe County is part of the Bloomington, Indiana, Metropolitan Statistical Area.

The mean center of the United States population is determined by the United States Census Bureau from the results of each national census. The Bureau defines it as follows:The concept of the center of population as used by the U.S. Census Bureau is that of a balance point. The center of population is the point at which an imaginary, weightless, rigid, and flat surface representation of the 50 states and the District of Columbia would balance if weights of identical size were placed on it so that each weight represented the location of one person. More specifically, this calculation is called the mean center of population.