Ilmer is a village and former civil parish, now in the parish of Longwick-cum-Ilmer, in Buckinghamshire, England. It is at the foot of the Chiltern Hills about 3 miles (5 km) northwest of Princes Risborough, near the boundary with Oxfordshire. In 1931 the parish had a population of 40.[1] On 1 April 1934 the parish was abolished to form "Longwick cum Ilmer".[2]