- December 8 – Darius T. Hicks is sentenced to life in prison for murdering Shawndre N. Fulton.
- December 14 – 28-year-old restaurant manager John M. Serumgard unintentionally kills himself in an early morning crash on Leesburg Pike in Falls Church when he loses control of the 2000 Ford Focus he is driving and strikes a tree, a light pole, and another tree.
- December 14 – The Herndon Official Worker Center opens amidst protests in Herndon.
- December 15 – 32-year-old Jairo F. Hernandez, his 3-year-old daughter Casandra, and her 6-year-old sister Maria Isabel Cruz die in a fire in the townhouse at 8064 Saint Annes Court in Alexandria.
- December 16 – 27-year-old Alirio Reyes is sentenced to life in prison by Federal judge T. S. Ellis, III for murdering 17-year-old Jose Sandoval on May 16, 2004.
- December 25 – Nathan Cheatham shoots his mother Sheila to death at their shared home in McLean, then drives to Great Falls, where he shoots Adam S. Price, Janina C. Price, and Christopher J. Buro before committing suicide.
- "Man Gets Life Sentence For Murder of Pregnant Girlfriend" The Washington Post: Focus on Fairfax. The Washington Post, 9 Dec. 2005. Web. 09 Nov. 2011.
- "Great Falls Man Dies in Car Accident." The Washington Post. WP Company, 15 Dec. 2005. Web. 04 June 2017.
- Aizenman, N. C., and Timothy Dwyer. "Words Fly at Day-Laborer Center in Herndon." Washington Post. The Washington Post, 15 Dec. 2005. Web. 11 Mar. 2012.
- "Three Fires, Three Deaths, Two Injuries." Connection Newspapers. Connection Newspapers, 21 Dec. 2005. Web. 17 June 2016.
- "MS-13 Member Gets Life in Prison." Washington Times. The Washington Times, 17 Dec. 2005. Web. 13 May 2014.
- Turque, Bill, and Maria Glod. "Before Va. Rampage, Mother Feared Son would Kill Self." The Washington Post: A.01. National Newspapers Core. Dec 28 2005. Web. 9 Nov. 2011
- McNeill, Brian. "McLean Man Kills Four, Self." McLean Connection. Connection Newspapers, 5 Jan. 2006. Web. 26 Nov. 2011.
|Fairfax County by Year: 2005|
|November 2005||·||December||·||January 2006|