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. to serve as housing for people working at theMartin Aerospace Company.