Ilchester is a village and civil parish, situated on the River Yeo or Ivel, five miles north of Yeovil, in the English county of Somerset. Originally a Roman town, and later a market town, Ilchester has a rich medieval history and was a notable settlement in the county; around the 12th and 13th centuries it was effectively the county town. It had, however, declined in size and importance by the beginning of the 18th century, and the last markets were held in 1833. In 1889 the historic corporation that had governed the town (the Bailiff and Burgesses) was dissolved.
The parish, which includes the former village of Sock Dennis, or Stock-Dennis, and the old parish of Northover, has a population of 2,153. Sock Dennis lies on the Monarch's Way long-distance footpath.