Old Mystic is a village[2] and census-designated place (CDP) located in the town of Groton, Connecticut, United States.

As of the census[4] of 2000, there were 3,205 people, 1,205 households, and 880 families residing in the CDP.

There were 1,249 housing units at an average density of 292.5 per square mile (112.9/km2).

The racial makeup of the CDP was 90.11% White, 2.43% African American, 0.66% American Indian, 3.43% Asian, 0.06% Pacific Islander, 0.50% from other races, and 2.81% from two or more races.

19.5% of all households were made up of individuals, and 5.1% had someone living alone who was 65 years of age or older.