The toponym is derived from the Old English for 'green hill near a wood', though the 'Underwood' part of the name was only added in the medieval period to differentiate the village from nearby Long Crendon and to signify the village's position close to the Bernwood Forest. The Domesday Book of 1086 records the village as Grennedone. The manor of Grendon anciently belonged to the St Amand family. Almeric de St Amand of this family was one of the godfathers of King Edward I, who was baptised in 1239. In 1642, Grendon Underwood lay on the forest tracks used by gypsies and strolling players and was visited more than once by William Shakespeare, who stayed at the house, formerly an inn, now known as Shakespeare House, currently a five star guest house and Grade II listed, part Elizabethan former coaching inn. Built in 1906, Grendon Underwood Junction was the point at Greatmoor, just east of Grendon Underwood village, at which the Alternative Route of the London Extension of the Great Central Railway left the original main line. This was a little north of the former Quainton Road railway station. The lines were closed to passenger trains in 1966 but subsequently used by freight trains. During the Second World War Grendon Hall was Station 53a of the Special Operations Executive. Roald Dahl’s mother Sophie had a cottage in Grendon Underwood. During WWII Sophie and her daughters moved here to escape the German bombings in London and eastern England. When Roald returned home from duty in the Royal Air Force in 1941 he at first had no idea where to find his family. Their eventual reunion is described by Dahl on the last page of his autobiography Going Solo.
Grendon Underwood has two prisons, both are remotely located one mile away from the church and main village. The B-Categoryprison HMP Grendon is the UK's only therapeutic community for the treatment of serious offenders. HMP Grendon opened in 1962 as an experimental prison for inmates with psychiatric antisocial personality disorder. The facility holds approx 238 cat B male prisoners. HMP Spring Hill is a D-Categoryopen prison with an operational capacity of 335 Indeterminate Sentenced Prisoners. The prison building, Springhill House was a former MI6 Secret Service base during the Second World War.
The Grendon Festival (GrendON)
This a Biennial event, with live music, comedians and a CAMRA supported real ale festival. The Grendon festival has a series of live tribute bands such as Kazabian, Noasis, Killerz, and Kings of Lyon, national and local bands such as Stoke Mandville Band, 48Krash. The festival, which takes place every other year, started out in 2006 with 300 people attending. In 2010 it attracted 2,000 and in 2012 organisers expected 4,000 attendees. However the event was postponed in May 2012 due to severe flooding and was successfully rescheduled to September 2012. The event was down-scaled for 2014 to include just 2 acts: "The Vinyls" and "Not the Rolling Stones", the event was expected to return to a mega-festival format in 2016, but was once again postponed.