Events that took place in Fairfax County in 1940:
- January 7 – Fulfilling his own prophecy of impending doom, 29-year-old tobacco salesman Sidney M. Little is beaten to death by 28-year-old Marine private Alexander J. Stevenson in a picnic area near the Fort Hunt CCC Camp in Alexandria.
- January 20 – 38-year-old Gustav E. Magnusson is fatally injured when he is struck by a car driven by 21-year-old John E. Peabody on Chain Bridge Road north of Langley. Peabody takes Magnusson, suffering from two broken legs and a fractured skull, to the Georgetown Hospital, where he is pronounced dead.
- February 4 – 28-year-old Archie W. Melvin is killed when he crashes the car he is driving into one driven by 37-year-old Thomas E. Everhart on the Leesburg Pike two miles west of Tyson's Corner.
- February 9 – Following an argument with his wife, 33-year-old farmer Medford G. Lick hangs himself in a barn on the Jouett Shouse estate near Vienna where he was a tenant.
- February 18 – 27-year-old Dee Marr VanCott is killed by an early morning fire that starts in his room at the Lord Fairfax Clubhouse at Mount Eagle. 32-year-old Richard Weedon unintentionally kills himself and fatally injures one of his passengers, 33-year-old Thomas Mercer, when he crashes into a telegraph pole on Franconia Road while chasing an engine of the Franconia Volunteer Fire Department on its way to fight the fire. Mercer is taken to Alexandria Hospital, where he dies that evening.
- April 6 – 32-year-old carpenter Stanley Webley is fatally shot in an alley beside the Herndon National Bank in Herndon.
- April 30 – 20-year-old Grace Jackson is strangled to death in a heavily forested Dike Woods area off Fort Hunt Road in Alexandria. Her nude body is discovered on May 2.
- July 1 - The Fairfax County Police Department becomes a separate law enforcement agency. Previously, the department had been part of the Fairfax County Sheriff's Office. The department consists of Chief Carl R. McIntosh, Detective Sergeant Henry T. Magarity, Traffic Sergeant Louis L. Finks, and Officers James Mahoney, James Dodson, and Alton Poole.
- October 27 – 57-year-old Susan Duffy, of New Castle, Delaware, dies when she loses control of her car and crashes into a dirt embankment along the Lee Highway. The crash also injures several members of Mrs. Duffy's family who were riding in the car with her.
- November 5 – Fairfax County voters reject a proposed change to the county's form of government to the executive form by nearly 4 to 1.
41 people were killed in traffic crashes in Fairfax County in 1940.
The population of Fairfax County in 1940 was 40,929.
- "Blood-Stained Death Car found in Garage at Triangle, Va." The Washington Post (1923-1954): 3. Jan 09 1940. ProQuest. Web. 19 Dec. 2017.
- "Virginian Gave Hint of Death before Slaying." The Washington Post (1923-1954): 3. Jan 10 1940. ProQuest. Web. 19 Dec. 2017.
- "2 Marines Given 15-Year Terms in Park Slaying." The Washington Post (1923-1954): 17. Jun 06 1940. ProQuest. Web. 19 Dec. 2017.
- "D. C. Man Is Killed By Auto; 4 Firemen Injured in Crash"Evening Star, 21 Jan. 1940, One Star, p. 2. NewsBank. Accessed 19 Dec. 2017.
- "Motorist Is Killed; 5 Hurt in Collision On Leesburg Pike" Evening Star, 5 Feb. 1940, Three Star, p. 17. NewsBank. Accessed 19 Dec. 2017.
- "Farmer a Suicide After Quarrel with Mother of 3." The Washington Post (1923-1954): 3. Feb 10 1940. ProQuest Historical Newspapers: The Washington Post (1877-1995). Web. 4 Sep. 2012.
- "3 Deaths Caused By Lord Fairfax Clubhouse Fire" Evening Star, 19 Feb. 1940, Three Star, p. 17. NewsBank. Accessed 19 Dec. 2017.
- "2 Arrested in Killing at Herndon." The Washington Post (1923-1954): 13. Apr 08 1940. ProQuest. Web. 26 Jan. 2017.
- Lacy, Sam. "Young Matron found Dead; Mate Sought." Afro-American (1893-1988): 11. May 04 1940. ProQuest. Web. 2 Feb. 2018.
- "Fairfax County Police Headed by McIntosh." The Washington Post (1923-1954): 13. ProQuest Historical Newspapers: The Washington Post (1877-1995). Jun 30 1940. Web. 23 Apr. 2012.
- "2 Die in Traffic; Truck Crash Fatal to Third in Family." The Washington Post (1923-1954): 1. ProQuest Historical Newspapers: The Washington Post (1877-1994). Oct 28 1940. Web. 27 Oct. 2011.
- "Fairfax Voters Reject Proposal to Change County Government" Evening Star, 6 Nov. 1940, Three Star, p. 26. NewsBank. Accessed 19 Dec. 2017.
- "Fairfax Reports 19 Traffic Deaths in 1941" Evening Star, 2 Jul. 1941, p. 23. NewsBank, . Accessed 28 Dec. 2017.
- "Historical Census Browser." University of Virginia Library. University of Virginia, n.d. Web. 30 Aug. 2014.
|Fairfax County by Year|