Its population was 1,430 in 1801, 4,049 in 1901 and 79,724 in 2001. The largest increase occurred in the 1950s and 1960s, after Stevenage was designated a new town under the New Towns Act of 1946.

Stevenage is served by the A1(M) motorway, taking traffic both north and south. It is also served by the smaller A602 road taking traffic southeast, meeting the A10 road at Ware.

It is also served by Stevenage railway station, sitting on the East Coast Mainline. As such regular trains to London are available.

The slow growth of Stevenage continued until, after the Second World War, the Abercrombie Plan called for the establishment of a ring of new towns around London. It was designated the first New Town on August 1946. The plan was not popular with local people who protested at a meeting held in the town hall before Lewis Silkin, minister in the Labour Government of Clement Atlee. As Lewis Silkin arrived at the railway station for this meeting, some local people had changed the signs 'Stevenage' to 'Silkingrad'. Ironically, although the New Towns Commission declared the Old Town would not be touched, the first significant building to be demolished in it was indeed the Old Town Hall, in which the opposition had been expressed.

In keeping with the sociological outlook of the day, the town was planned with six self-contained neighbourhoods. The first two of these to be occupied were the Stoney Hall and Monks Wood "Estates" in 1951. Next to be built and occupied was Bedwell in 1952 - The Twin Foxes pub was Stevenage's first "new" public house and is still situated in the Bedwell estate. The public house was named after local notorious identical twin poachers (Albert Ebenezer and Ebenezer Albert Fox). Next came Broadwater and Shephall (1953), then Chells in the 1960s and later Pin Green and Symonds Green. Early occupants came from London 'overspill'. Another area, (currently under construction) is Great Ashby, which will be completed in 2008.

At least two other public houses are worth mentioning, for they have got a direct relationship to local history: The name of the pub "Edward the Confessor"(closed 2006) could have a connection to the time in which the St Mary Church in nearby Walkern was built, for King Edward ruled from 1042 until his death in 1066. Walkern's village church dates from this time. The second pub with a strong bond to local history seems to be the "Our Mutual Friend" in Shephall, for the name of the pub is the title of a novel by Charles Dickens. Dickens was at some occasion guest to Sir Edward Bulwer-Lytton in nearby Knebworth House, and for that reason he knew Stevenage very well.

Famous people from Stevenage

• Ian Allinson (b. 1957), footballer (born in Stevenage)
• Harry Bates (1850–1899), sculptor (born in Stevenage)
• Andrew Croft (1906-1991) explorer and SOE (Special Operations Executive) agent (born in Stevenage)
• Francis Cammaerts (1916–2006), headmaster of Alleyne's Grammar School and witness in the Lady Chatterley Trial, October 1960
• Denholm Elliott (1922–1992), actor, who lived in the house now known as the 'Little Folks Lab' nursery in the North-West of the town
• Fields of the Nephilim, goth band
• Barbara Follett (b. 1942), politician
• Ken Follett (b. 1949), author
• Albert and Ebenezer Fox (1857–1926, 1857–1936), infamous poachers (born in Stevenage)
• Lewis Hamilton (b. 1985), Formula One world champion (born in Stevenage)
• Alex Pettyfer (b. 1990), actor (born in Stevenage)
• Kevin Phillips (b. 1973), footballer
• Ian Poulter (b. 1976), golfer
• Jason Shackell(b. 1983), footballer (born in Stevenage)
• Naum Slutzky (1894-1965], designer, master of Weimarer Bauhaus
• John Thurloe (1616–1668), secretary to Oliver Cromwell, lived in what is now the Cromwell Hotel.
• Henry Trigg, 18c. farmer who wanted to come back from the dead after 30 years. His coffin was placed on a beam in a barn which later became a bank in Old Stevenage.
• Ed Westwick (b. 1987), actor (born in Stevenage)
• Ashley Young (b. 1985), footballer (born in Stevenage)
• Rob Playford (b. 1968), Drum and Bass Pioneer and founder of Moving Shadow Records
• Edward Gordon Craig, theatrical designer and artist
• Rupert Grint (b. 1988), actor
• Anthony (Tony) John Wright (b. 1962), cricketer