Resident Population in Jefferson County, CO was 576.36600 Thous. of Persons in January of 2023, according to the United States Federal Reserve. Historically, Resident Population in Jefferson County, CO reached a record high of 583.05000 in January of 2020 and a record low of 235.36800 in January of 1970. Trading Economics provides the current actual value, an historical data chart and related indicators for Resident Population in Jefferson County, CO - last updated from the United States Federal Reserve on May of 2024.