Middle River is an unincorporated community and census-designated place in Baltimore County, Maryland, United States. The population was 25,191 at the 2010 census. A Middle River Train Station first appears on the 1877 G.M. Hopkins & Co Baltimore County Map and by 1898 has a designated Post Office and modest street grid. The town expanded during the 1930s and 1940s and established the "Aero Acres" housing community which borders the railroad tracks and Martin Blvd.