National CSS, Inc. (NCSS) was a time-sharing firm in the 1960–80s, until its acquisition by Dun & Bradstreet in 1979. NCSS was originally headquartered in Norwalk, Connecticut, but relocated to Wilton in 1978. Sales offices, data centers, and development facilities were located at various sites throughout the U.S. Some additional sales offices were active in the UK and elsewhere.