In 2013, the county had a population of 1,140,700 living in an area of 634 square miles (1,640 km2). Four towns have between 50,000 and 100,000 residents: Hemel Hempstead, Stevenage, Watford and St Albans. Hertford, once the main market town for the medieval agricultural county, derives its name from a hart (stag) and a ford, used as the components of the county's coat of arms and flag. Elevations are high for the region in the north and west. These reach over 800 feet (240 m) in the western projection around Tring which is in the Chilterns. The county's borders are approximately the watersheds of the Colne and Lea; both flowing to the south; each accompanied by a canal. Hertfordshire's undeveloped land is mainly agricultural and much is protected by green belt.
The county's landmarks span many centuries, ranging from the Six Hills in the new town of Stevenage built by local inhabitants during the Roman period, to Leavesden Film Studios. The volume of intact medieval and Tudor buildings surpasses London, in places in well-preserved conservation areas, especially in St Albans which includes some remains of Verulamium, the town where in the 3rd century an early recorded British martyrdom took 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 background is reflected in the flag and coat of arms of Hertfordshire.
Hertfordshire is well-served with motorways and railways, providing good access to London. The largest sector of the economy of the county is in services.
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.