Resident Population in Middlesex County, CT was 164.75900 Thous. of Persons in January of 2021, according to the United States Federal Reserve. Historically, Resident Population in Middlesex County, CT reached a record high of 166.19900 in January of 2011 and a record low of 115.01800 in January of 1970. Trading Economics provides the current actual value, an historical data chart and related indicators for Resident Population in Middlesex County, CT - last updated from the United States Federal Reserve on May of 2024.