Middlesex County is located in the south central part of the U.S. State of Connecticut. As of the 2020 census, the population was 164,245. 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.