Fairfield County is a county in the southwestern corner of the U.S. state of Connecticut. It is the most populous county in the state and was also its fastest-growing from 2010 to 2020. As of the 2020 census, the county's population was 957,419, representing 26.6% of Connecticut's overall population. The closest to the center of the New York metropolitan area, the county contains four of the state's top 7 largest cities—Bridgeport (1st), Stamford (2nd), Norwalk (6th), and Danbury (7th)—whose combined population of 433,368 is nearly half the county's total population.

Connecticut is the southernmost state in the New England region of the Northeastern United States. It borders Rhode Island to the east, Massachusetts to the north, New York to the west, and Long Island Sound to the south. Its capital is Hartford, and its most populous city is Bridgeport. Connecticut lies between the major hubs of New York City and Boston along the Northeast Corridor, where the New York metropolitan area, which includes six of Connecticut's seven largest cities, extends well into the southwestern part of the state. Connecticut is the third-smallest state by area after Rhode Island and Delaware, and the 29th most populous with slightly more than 3.6 million residents as of 2020, ranking it fourth among the most densely populated U.S. states.