Eggenwil is first mentioned about 1160 as "Egenwilare" in a donation document, the "Acta Murensia". The village and church were given by Albert II, Count of Habsburg (died 1140) to Muri Abbey. However, the Habsburg rights of Low justice were given to the Hermetschwil abbey. In 1415 the Aargau was taken from the Habsburgs by the Swiss Confederates. While Bern kept the southwest portion (Zofingen, Aarburg, Aarau, Lenzburg, and Brugg). Some districts, named the "Freie Ämter" or "free bailiwicks", with the County of Baden, were governed as "subject lands" by all or some of the Confederates. Part of Eggenwil was transferred to the "Amt Hermetschwil" of the "Freie Ämter", and the portions of the village north of the main road became part of the County of Baden. During the Helvetic Republic (1798–1803) Eggenwil and Widen formed a single municipality. Since the end of the Helvetic Republic, Eggenwil has been an independent municipality 1798-1803.