- December 9 – 27-year-old motorcycle enthusiast Ronald W. Pryor is convicted of abduction and second-degree murder for the LSD-inspired killing of 22-year-old Marine Corporal Walley L. Gaddis, Jr. in Lorton on May 29, 1969.
- December 10 – 22-year-old Carson Kennedy is fatally wounded when he is shot in the throat with a .38 caliber revolver during a dispute with 35-year-old Estel E. Rohrbaugh at the ARCO gas station at the intersection of Route 1 and Gunston Road in Lorton. Kennedy is taken to the DeWitt Army Hospital on Fort Belvoir, where he is pronounced dead about an hour later.
- December 21 – 19-year-old Intesar A. Amra is shot to death in Centreville. Her body is found a few hours later in a clearing under some power lines about 25 feet away from Pleasant Valley Road by passerby Harold Seal.
- December 23 – Columnist David Lawrence donates a large tract of land from the estate of his late wife, Ellanor C. Lawrence, to Fairfax County for use as a public park. The tract, located in the western part of the county and about a square mile in size, will become the core of the Ellanor C. Lawrence Park.
- December 27 – 50-year-old convicted murderer William P. Sikes asphyxiates himself with gas in the laundry at the Fairfax County Jail.
- December 29 – 63-year-old Amos C. Seal, Jr. is killed in the garage of the Schultz Construction Company at 564 Spring Street in Herndon when the fan blade of a pickup truck's radiator breaks and strikes him in the throat. Seal is taken to Fairfax Hospital, where he is pronounced dead.
- Curry, William N. "'LSD Tripper' Guilty in Marine's Death." The Washington Post, Times Herald (1959-1973): 1. Dec 10 1970. ProQuest.Web. 24 Aug. 2016 .
- "Fairfax Man Shot Dead at Gas Station." The Washington Post, Times Herald (1959-1973): 1. Dec 12 1970. ProQuest. Web. 1 Jan. 2018.
- Bredemeier, Kenneth. "Jordanian Woman found Slain Near Road in Fairfax." The Washington Post, Times Herald (1959-1973): 1. Dec 22 1970. ProQuest. Web. 30 Apr. 2014.
- Bredemeier, Kenneth. "Fairfax Gets Gift of Land." The Washington Post, Times Herald (1959-1973): D1. ProQuest Historical Newspapers: The Washington Post (1877-1995). Dec 24 1970. Web. 23 Feb. 2012.
- "Man Who Killed Wife Commits Suicide in Jail" Evening Star, 28 Dec. 1970, Three Star NIGHT FINAL, p. 23. NewsBank. Accessed 15 Jan. 2018.
- Ringle, Ken. "Slayer of Wife Kills Self." The Washington Post, Times Herald (1959-1973): 1. Dec 29 1970. ProQuest. Web. 15 Jan. 2018.
- "Mishap Kills Truck Repairer." The Washington Post, Times Herald (1959-1973): 1. Dec 31 1970. ProQuest. Web. 17 Jan. 2018.
- "Broken Fan Blade Fatally Strikes Herndon Worker" Evening Star, 31 Dec. 1970, Three Star NIGHT FINAL, p. 21. NewsBank. Accessed 17 Jan. 2018.
|Fairfax County by Year: 1970|
|November 1970||·||December||·||January 1971|