1866 in sports describes the year's events in world sport.
- Foundation of Upton Park F.C.
- The Amateur Athletics Club (AAC) is founded and becomes the governing body of athletics in the United Kingdom, hosting the first national championships and introducing a definition of "amateur" that will determine eligibility for athletics competitions until the late 20th century.
- 6 August — Jem Mace defeats Joe Goss in the 21st round and reclaims the vacant English Championship.
- 19 September — Mike McCoole defeats Bill Davis in the 34th round at Rhodes Point, near St Louis, and underlines his claim to the American Championship. The third claimant Jimmy Elliott does not fight anyone this year.
- George Wootton's tally of 119 wickets establishes a new record for an English season.
- Grand National – Salamander
- 1,000 Guineas Stakes – Repulse
- 2,000 Guineas Stakes – Lord Lyon
- The Derby – Lord Lyon
- The Oaks – Tormentor
- St. Leger Stakes – Lord Lyon
- Melbourne Cup – The Barb
- Queen's Plate – Beacon
- Irish Derby Stakes – Selim
The Boat Race
The American schooners Vesta, Henrietta and Fleetwing cross the Atlantic Ocean from Sandy Hook to the Needles, Isle of Wight in the first organised offshore race. The Henrietta, owned by 21-year-old James Gordon Bennett, Jr., and captained by Samuel S. Samuels won the race in 13 days, 21 hours and 55 minutes.
- Cyber Boxing Zone – Jem Mace. Retrieved on 8 November 2009.
- Cyber Boxing Zone – Mike McCoole. Retrieved on 8 November 2009.
- Cyber Boxing Zone – Jimmy Elliott. Retrieved on 8 November 2009.
- "Epsom Derby | History, Winners, & Facts | Britannica". www.britannica.com. Retrieved 28 December 2021.