Charterhouse Square is a historic square in Smithfield, central London. It lies between Charterhouse Street and Clerkenwell Road, in the extreme south of the London Borough of Islington, just north of the City of London.
In 1371 a Carthusian monastery was founded by Walter de Manny on what is now the north side of the square. It was established near a 1348 plague pit, which formed the largest mass grave in London during the Black Death, and tens of thousands of bodies were buried there. The name of the monastery, Charterhouse, was derived as an Anglicisation of La Grande Chartreuse, whose order founded the monastery.
The Charterhouse was dissolved as a monastery in 1537, and in 1545 was purchased by Sir Edward (later Lord) North (c. 1496-1564) and transformed into a mansion house. Following North's death, the property was bought by Thomas Howard, 4th Duke of Norfolk, who was imprisoned there in 1570 after scheming to marry Mary, Queen of Scots. Later, Thomas Sutton bought the Charterhouse, and on his death in 1611, endowed a hospital (almshouse) and school on the site, which opened in 1614, supporting 80 pensioners (known as 'brothers'). The school for boys coexisted with the home for pensioners until 1872 when Charterhouse School moved to Godalming in Surrey. Following this, the Merchant Taylors' School occupied the buildings until 1933. The square also lends its name to a preparatory school which occupies a building overlooking the square.