Jefferson County, Colorado. Real estate Colorado Board of Health urges Jeffetson County to stop approving land developments near Rocky Flats. Details. RMN D 18, 1975 p.5 Post D 18, 1975 p.21 County Commissioners misinformed about the economic impact report before they approved plans for 1,900 acre development along I-470 corridor. RMN Ja 27, 1976 p.1 Post Ja 27, 1976 p.17 Jefferson County commissioner says economic impact statement on a 1,900 acre development along the I-470 corridor does exist.- RMN F 4, 1976 p.55