The name Runnymede is used commonly now to refer to land in National Trust ownership in the Thames flood plain south-west of the river between Old Windsor and Egham. The area comprises Long Mede and Runnymede which with Coopers Hill Slopes is managed by the National Trust, and Yard Mede.

The countryside is characterised as "Thames Basin Lowland" typified by gently rolling hills, ponds, meadows and woods. The National Trust area is a Site of Nature Conservation Interest (SNCI) which contains a Site of Special Scientific Interest. These are overseen by Runnymede Borough Council.

The National Trust holding encompasses 188 acres donated in 1929 by the first Lady Fairhaven and her two sons in memory of Urban Hanlon Broughton; and 110 acres of broadleaved woodland on Coopers Hill Slopes given in 1963 by Egham Urban District Council. (In April 1974 the Council was subsumed within Runnymede Borough.)

Near Magna Carta Island on the north-east flood plain in park land are Ankerwycke and the ruins of the 12th Century Priory of St Mary's. The Thames has changed course regularly and these areas may once have been an integral part of Runnymede and except for Magna Carta Island were acquired by the National Trust in 1998.