The name Ilsley appears to be derived from Hilde-Laege meaning “Place of Conflict”. One of the villages bearing this name is therefore thought to be the site of the Battle of Ashdown (AD 871) which is known to have taken place somewhere on the Downs. It was here that Prince (later King) Alfred won his magnificent victory over the invading Danish armies; though there are good reasons for supposing this took place in adjoining East Ilsley.

The Italian Archbishop, Marco Antonio de Dominis, was a resident in the village from 1616 after leaving Rome due to a row with the Pope. He searched local leases for legal loopholes which enabled him to extract some £1,600 from the tenants. The villagers eventually complained to the Church and he returned to Rome, where he was tortured by the Inquisition.

Prior to the Civil War, the villagers met on the Downs near this village to discuss the hardships imposed upon them by the King. They decided to petition him for exemption. In 1644, Charles I was actually entertained, at the Rectory here, by the rector, Dr. Godfrey Goodman. He paid dearly for his loyalty for he was ousted from his position by the civil authorities two years later.

William of Orange and his Dutch troops passed this way whilst on the march towards Reading and then London where he was to take the throne as William III.

West Ilsley was the original home of the Morland Brewery of Abingdon - now owned by Green King, but remembered in their Morland Original and Old Speckled Hen brands of beer. John Morland, a local farmer, started brewing in 1711 and his ale and porter became much sought after in London's pubs. The business was only relocated to Abingdon in 1887.