Adelsö kyrka has medieval origins, with the surviving stone church believed to date from the end of the 1100s. Given the site's historical importance as a royal estate, it is thought likely that an earlier wooden church once stood here, though no physical trace of it has been found. Just north of the church lie three large burial mounds, further evidence of an early royal presence, and the adjoining area of Hovgården is now recognised as a World Heritage Site.
The church was probably built on royal initiative to serve both the parish and the nearby royal manor of Alsnö hus. It originally consisted of a nave with a narrower, lower chancel ending in a semicircular apse. Traces of this apse were rediscovered and exposed during a 1957 renovation and remain marked at the east wall of the chancel. A sacristy was added north of the chancel in the 1300s, complete with a brick vault from the outset.
Over later centuries the building changed considerably. A tower was added, probably in the early 1400s, and by the mid-1400s its ground floor had been linked to the main church space, both parts then receiving brick vaulting. In the 1470s the chancel was widened and merged with the nave to create a single-hall church, with a star vault added over the new chancel, while a timber porch was built on the south side.
Further changes followed: the timber porch, said to have suffered a fire at some point before 1679, was later rebuilt, and the tower gained its current spire during an 18th-century rebuilding. A significant renovation in 1823 removed the south porch entirely and relocated the main entrance to its present position on the west side of the tower, where it remains.
Inside, visitors can see a plain sandstone font from the late 1100s and two crucifixes, one from the second half of the 1300s hanging above the sacristy entrance, and another from the late 1400s displayed within the sacristy itself. The altarpiece, carved in wood in the shape of a sarcophagus, dates from 1802, while the pulpit was installed in 1786. The church's mechanical organ was built in 1829 by Pehr Zacharias Strand of Stockholm and was later restored to its original specification.