The earliest known stone church on this site was modest in scale, with a nave measuring roughly 4.8 by 9 metres and a tower some 3.6 metres square and about 13.2 metres high. Despite its diminutive proportions, the church's name is not thought to refer to its size but rather to its proximity to Glanshammar, the largest church in the hundred (administrative district) during the medieval period.
The building evolved considerably over the centuries. Originally constructed with a west tower and a narrower chancel to the east, it was remodelled into a hall church during the late medieval period and fitted with vaulting. A major rebuilding in 1637–1638, funded by Carl Bonde, widened the church to its present breadth and gave it a two-aisled form. Sources agree on this campaign, though the church's overall dimensions after rebuilding are given as approximately 18 by 10.8 metres. In 1781 the church was further lengthened to the east and a sacristy added, a phase during which the earlier vaults were removed. The present west tower dates from 1829.
The church's furnishings include an organ with a layered history. An instrument of five stops was donated in 1672 by the provincial governor Abraham Leijonhufvud, though it reportedly stood unusable for several decades before being repaired and enlarged in 1761. A later organ of seven stops was built in 1893 by the Örebro firm E A Setterquist & Son, and the current instrument, also by Setterquist & Son, dates from 1967.
Visitors interested in the building's long architectural evolution — from a tiny Romanesque church, through medieval vaulting and a seventeenth-century widening, to its final eastward extension and new tower — will find Lillkyrka a compact but layered example of Swedish parish church development spanning over eight centuries.