Guilford is a town in New Haven County, Connecticut, United States, that borders Madison, Branford, North Branford and Durham, and is situated on I-95 and the Connecticut seacoast. The population …Guilford is a town in New Haven County, Connecticut, United States, that borders Madison, Branford, North Branford and Durham, and is situated on I-95 and the Connecticut seacoast. The population was 22,073 at the 2020 census.