| Cessy | |
| Commune Status: | Commune |
| Image Coat Of Arms: | Blason ville fr Cessy 01.svg |
| Arrondissement: | Gex |
| Canton: | Gex |
| Insee: | 01071 |
| Postal Code: | 01170 |
| Mayor: | Christophe Bouvier[1] |
| Term: | 2020 - 2026 |
| Intercommunality: | CA Pays de Gex |
| Coordinates: | 46.3192°N 6.07°W |
| Elevation M: | 526 |
| Elevation Min M: | 496 |
| Elevation Max M: | 583 |
| Area Km2: | 6.39 |
Cessy (in French pronounced as /sesi/) is a commune in the Ain department in eastern France. The area was first inhabited by two farming families in the eleventh century, and as the town has grown its agricultural heritage has remained a significant feature, with the populated area surrounded by a vast expanse of fields and an annual agricultural festival.
Cessy has an oceanic climate (Köppen climate classification Cfb). The average annual temperature in Cessy is . The average annual rainfall is with December as the wettest month. The temperatures are highest on average in July, at around, and lowest in January, at around . The highest temperature ever recorded in Cessy was on 13 August 2003; the coldest temperature ever recorded was on 1 February 2003.
See main article: Compact Muon Solenoid. One of the primary points of interest in the quiet community of Cessy, France is the Compact Muon Solenoid (CMS) experiment, located 100 meters below ground at a site on the south-eastern edge of the village. CMS is a high-energy particle physics experiment which observes the result of high energy proton-proton collisions of the CERN laboratory's Large Hadron Collider (LHC) particle accelerator.[2]
Tim Berners-Lee lived on Rue de la Mairie in Cessy when he, with Robert Cailliau, invented the World Wide Web.