Middlesex County is located in the south central part of the U.S. state of Connecticut. As of 2000 the population was 155,071. As is the case with all eight of Connecticut's counties, there is no county government, and no county seat. In Connecticut, towns are responsible for all local government activities, including fire and rescue, snow removal and schools. In a few cases, neighboring towns will share certain resources, i.e. water, gas, etc. However, Middlesex County is merely a group of towns on a map, and has no particular authority.

As of the census˛ of 2000, there were 155,071 people, 61,341 households, and 40,607 families residing in the county. The population density was 162/km˛ (420/mi˛). There were 67,285 housing units at an average density of 70/km˛ (182/mi˛). The racial makeup of the county was 91.28% White, 4.42% Black or African American, 0.17% Native American, 1.56% Asian, 0.04% Pacific Islander, 0.97% from other races, and 1.56% from two or more races. 3.00% of the population were Hispanic or Latino of any race.