The present church was consecrated in 1864, after which the old medieval wooden church was pulled down, in October 1865. That earlier building was a small pine-log structure with a shingle roof, painted red, with a modest porch and bell tower; it had been extended eastwards in 1759, roughly doubling its size. Until 1902 the new stone church was known as Varnum, since it also served the neighbouring Vara parish until Vara's own church was completed, at which point the older name Önum was restored.
Built of stone with a slate roof and a copper-clad tower, the church shows a Gothic Revival character in its apse, spire, panelled ceiling and pulpit — stylistic flourishes typical of the period rather than genuine medieval work. A substantial renovation in 1948, overseen by Axel Forssén, removed a wall that had screened off an earlier sacristy in the apse, replaced the old stoves with electric heating, and reworked the original pews for comfort.
Among the furnishings is an oak altar cabinet with a carved Madonna figure standing on a crescent moon, dated to around the 1500s; the Madonna herself stands 72 cm tall within a cabinet 162 cm wide, and the piece was conserved in 1934–35. The font is medieval, though its base has been renewed after the original eroded. The pulpit is Baroque, probably dating from around 1700. The organ, built in 1945 by Hammarbergs Orgelbyggeri, retains the silent facade of its 1878 predecessor by Salomon Molander.
Of the medieval church nothing remains on site but a stone wall enclosing a disused churchyard, marked by four grave crosses and a memorial stone. A fragment of a wooden log bearing a runic inscription, interpreted as recording that a man named Olof built the church, survives and is held by the Swedish History Museum; the archaic character of the script suggests an early medieval date for the original building.
The churchyard also contains graves connected with a reported drowning accident in which children fell through ice on a nearby dam; local tradition names some of those who died, and at least one grave, marked by a memorial tree, is said to commemorate a young girl. Details of this story rest on oral tradition and should be treated as such rather than as settled fact.