Watford Mencap was started in 1951 by a group of local parents as a local group of the Hertfordshire Branch of the National Association of Parents of Backward Children, which had been created in 1950.

In 1955 the National Association was changed to The National Society for Mentally Handicapped Children and local groups were formalised. During the sixties Watford Mencap was at the forefront of actively campaigning for services nationally, while also developing services of their own.

The “Stepping Stones Club” was opened in September 1956 for children aged 10 upwards and was followed by the Tuesday Club in 1960 for those aged 16 plus. In 1962 Watford Round Table agreed to raise money for the purchase of St Matthew's Church Hall (Table Hall) which enabled the organisation to use the facility for nursery groups, meetings and fundraising activities.

By the end of the 1970s the Society had purchased 2 properties with a view to providing supported accommodation for people with learning disabilities. The first play scheme for special needs children had run, along with a weekly club for older children.

The organisation became known has Watford & District Mencap and grew again during the 1990’s with a small office opening in Rickmansworth, 3 more properties for supported living as well as other community services being started including the Community Support Service, Advice & Advocacy Service, Children’s Services and Leisure Together.

In 2005 the organisation moved to change its name to Watford Mencap and to lose the link with the phrase 'mentally handicapped'. The Head Office moved to larger premises in Rickmansworth and the organisation took over the facilitation of 5 Speaking Up groups throughout South West Hertfordshire.

Change continued to be part of Watford Mencap, with another move for the Head Office to the Old Town Hall in 2009. The organisation is still at the forefront of innovation, supporting people to access Individual Budgets and personalisation.