Hertfordshire was the area assigned to a fortress constructed at Hertford under the rule of Edward the Elder in 913. Hertford is derived from the Anglo-Saxon heort ford, meaning deer crossing (of a watercourse). The name Hertfordshire is first recorded in the Anglo-Saxon Chronicle in 1011. Deer feature in many county emblems.
There is evidence of humans living in Hertfordshire from the Mesolithic period. It was first farmed during the Neolithic period and permanent habitation appeared at the beginning of the Bronze Age. This was followed by tribes settling in the area during the Iron Age.
Following the Roman conquest of Britain in AD 43, the aboriginal Catuvellauni quickly submitted and adapted to the Roman life; resulting in the development of several new towns, including Verulamium (St Albans) where in c. 293 the first recorded British martyrdom is traditionally believed to have taken place. Saint Alban, a Romano-British soldier, took the place of a Christian priest and was beheaded on Holywell Hill. His martyr's cross of a yellow saltire on a blue field is reflected in the flag and coat of arms of Hertfordshire as the yellow field to the stag or Hart representing the county. He is the Patron Saint of Hertfordshire.
With the departure of the Roman Legions in the early 5th century, the now unprotected territory was invaded and colonised by the Anglo-Saxons. By the 6th century the majority of the modern county was part of the East Saxon kingdom. This relatively short lived kingdom collapsed in the 9th century, ceding the territory of Hertfordshire to the control of the West Anglians of Mercia. The region finally became an English shire in the 10th century, on the merger of the West Saxon and Mercian kingdoms.
A century later, William of Normandy received the surrender of the surviving senior English Lords and Clergy at Berkhamsted, resulting in a new Anglicised title of William the Conqueror before embarking on an uncontested entry into London and his coronation at Westminster. Hertfordshire was used for some of the new Norman castles at Bishop's Stortford, and at King's Langley, a staging post between London and the royal residence of Berkhamsted.
The Domesday Book recorded the county as having nine hundreds. Tring and Danais became one—Dacorum—from Danis Corum or Danish rule harking back to a Viking not Saxon past. The other seven were Braughing, Broadwater, Cashio, Edwinstree, Hertford, Hitchin and Odsey.
The first shooting-down of a zeppelin over Great Britain during WW1 happened in Cuffley.
As London grew, Hertfordshire became conveniently close to the English capital; much of the area was owned by the nobility and aristocracy, this patronage helped to boost the local economy. However, the greatest boost to Hertfordshire came during the Industrial Revolution, after which the population rose dramatically. In 1903, Letchworth became the world's first garden city and Stevenage became the first town to redevelop under the New Towns Act 1946.
From the 1920s until the late 1980s, the town of Borehamwood was home to one of the major British film studio complexes, including the MGM-British Studios. Many well-known films were made here including the first three Star Wars movies (IV, V, & VI). The studios generally used the name of Elstree. American director Stanley Kubrick not only used to shoot in those studios but also lived in the area until his death. Big Brother UK and Who Wants To Be A Millionaire? have been filmed there. EastEnders is filmed at Elstree. Hertfordshire has seen development at Warner Bros. Studios, Leavesden; the Harry Potter series was filmed here and the 1995 James Bond film GoldenEye.
On 17 October 2000, the Hatfield rail crash killed four people with over 70 injured. The crash exposed the shortcomings of Railtrack, which consequently saw speed restrictions and major track replacement. On 10 May 2002, the second of the Potters Bar rail accidents occurred killing seven people; the train was at high speed when it derailed and flipped into the air when one of the carriages slid along the platform where it came to rest.
In early December 2005, the 2005 Hemel Hempstead fuel depot explosions occurred at the Hertfordshire Oil Storage Terminal.
In 2012, the canoe and kayak slalom events of the 2012 Summer Olympic Games took place in the town of Waltham Cross, within the borough of Broxbourne.