It rises near Hellidon, Northamptonshire and flows southwards for 40 miles (64 km) to meet the Thames at Oxford in Oxfordshire.

Helidon Hill, immediately north, forms a watershed: on the south side, the Cherwell feeds the Thames, in turn the North Sea; opposite, the Leam feeds the Warwickshire's Avon through Worcestershire into the Severn, the head of the Bristol Channel.

The Cherwell skirts the east side of Cropredy itself and passes under Cropredy Bridge, site of a major battle of the English Civil War in 1644, a long encounter with riverside skirmishes concentrated along 3 miles (4.8 km) of bank between Hay's bridge and a ford at Slat Mill near Great Bourton.

This line was built by the Great Western Railway and links London and Oxford with Birmingham and the north.

The brick-built building and miller's cottage have been modernised and extended as Banbury's main theatre and arts centre.

By the weir the railway's older line continues down the valley to Oxford; east of it, a more direct route (opened in 1910 by the Great Western Railway) runs via Bicester and High Wycombe to London, originally connecting Paddington station, succeeded by London's newest main terminus, Marylebone.

That at Lower Heyford (noted as pre-Conquest and in 1086 there in the Domesday Book) was last rebuilt in the early 19th century, milling until 1946.

At Rousham, the river passes a famous landscape garden designed by William Kent.

The Cherwell passes under the Woodstock to Bicester road and shortly after the Oxford Canal flows into it from the east.

East of Shipton, the deserted village of Hampton Gay fronted the river, main remnants being its disused church in the watermeadows and ruins of a manor house.

In hills to the east, a Romano-British settlement stood near Kidlington and a contemporary villa in a west-bank parish, Islip.

[citation needed] To its east is a wide plain, Otmoor, drained by the multi-headwater Ray, the largest tributary, which joins at a weir in Islip, known as The Stank.

Parson's Pleasure and Dame's Delight were for typically nude bathing for men and women respectively, now defunct.

One is Mesopotamia, which is a long thin island just south of the Parks with a scenic, tree-lined path.

The river then skirts Christ Church Meadow before flowing into the Thames (or Isis) through two branches; the island in between has the main shared college boathouses for rowing.

(A punt is a long, flat-bottom, low-topsides, boat propelled by a pole pushed against the river bed.)

The river is known as the divide of the Dobunni to the west and the Catuvellauni to the east (Celtic tribes documented at the time of Romanisation).

At Oxney, Oxford a Romano-British settlement grew up, being naturally protected from raids by the large rivers.

This settlement dominated the pottery trade in what is now central southern England, distributing it by boats on the Thames and its tributaries.

Since the opening of the Oxford Canal in 1790 only a few sections are navigable, mainly to canoes and punts of shallow draft.

Tolkien's son John suggests that the drawing was based on one of the few unpollarded willows on the Cherwell at Oxford.