Middlesex County is located in the south central part of the U.S. State of Connecticut. As of the 2010 census, the population was 165,676. The county has a total area of 1,137 km² (439 mi²). 956 km² (369 mi²) of it is land and 181 km² (70 mi²) of it is water. The total area is 15.90% water.