The County School for Boys, Wallington opened on the 19th September 1927, the 33rd birthday of Mr W.T.Hutchins, its first Headmaster.  There were just 71 pupils when the school opened at its original site in Queen’s Road, Wallington. To join the school, boys had to pass an entrance examination, or win a county scholarship and parents had to pay the not inconsiderable sum of £3 per term. The school moved to its present site in 1935.

The outbreak of war led to a time of crisis for the school.  In February 1944, a bomb exploded outside the senior cloakroom and demolished a section of the building. Four months later, a flying bomb landed near Bunker’s Alley, breaking nearly every window in the school and causing widespread damage. The Headmaster refused to close the school and emergency repairs made it possible for a few rooms to be used. Additional accommodation was provided at Carew Manor, which was to become the home of the lower school until 1972.

Following the introduction of grammar schools in the 1944 Education Act, the school became known as Wallington County Grammar School for Boys.

In 1959, a new block was opened, providing extra laboratories, classrooms, a canteen and a dining room. 1973 saw the completion of the Sixth Form Block. In 1996, the school’s new science block was opened by Sir Chris Woodhead, an Old Boy of the School and, at the time, Her Majesty’s Chief Inspector of Schools. A second phase was completed in 2000 and was further enhanced in 2004, when the school was awarded ‘Science College’ status.

In 2009, the school was awarded High Performing Specialist School status and gained a second specialism in Applied Learning.

The school completed the building of a new sports hall in 2010. This welcome addition provides excellent changing facilities, a large indoor sports area and a weights training room. 

The school is blessed by the long service of its headmasters. Mr Hutchins, the founding Headmaster, served the school for 32 years. He was succeeded in 1959 by Mr Hitchin, who served for 17 years before handing over to Mr Harrison, whose 14 year stint was exceeded by Dr Haworth, who began his headship in 1990 and served for 20 years. More recently, Mr Smart became Headmaster in 2010 until his retirement in 2013, when Mr Wilden assumed the role. During Mr Wilden's tenure, the school became part of Folio Education Trust, which joined Greenshaw Learning Trust in 2024. Mr Bean has led the school since June 2016. 

The former students of Wallington County Grammar School are known as ‘Old Walcountians’.  The Association was formed in 1933 and retains close links with the school. The ‘Old Walcountians’ Dining Club’ meets annually and was formed following a dinner held in 1967 to commemorate the knighthood conferred on a distinguished Old Boy, Douglas Allen, later elevated to Lord Croham. The Old Walcountians’ Association leases the school's 30 acres of sports grounds at Clock House in Woodmansterne, which include a floodlit, all-weather hockey pitch. The Association attracts mainly Old Boys, and more recently, Old Girls, who wish to remain active in a wide range of sports.