The original church at Fellingsbro dates from the 1100s or 1200s, but it was substantially enlarged in the 1500s to reach roughly its present size. Its current appearance, however, owes much to alterations made in the 1800s. The building's sheer scale and the richness of its furnishings reflect a time when Fellingsbro parish was among the wealthiest in the country, so sought-after that the poet Esaias Tegnér was among those who applied for its living.
Inside, visitors will find a baroque altarpiece and pulpit of considerable splendour, along with a large font set apart by an ornate wrought-iron screen. The bright, spacious interior, with its columns and accumulated treasures, has been likened to a church interior one might expect to find in Rome rather than in the Swedish countryside.
Two bells dating from the 1400s still hang in the tower. According to local tradition, the parish paid a ransom in silver to keep these bells from being confiscated by Gustav Vasa during the Reformation-era seizures of church property.
Beside the church stands a substantial medieval stone tower known as the kastalen, part of which now serves as a museum. Despite its fortress-like appearance, historians are uncertain whether the tower ever had a genuine defensive function; it is thought more likely to have served as a tithe barn, and it has at various times also been used as a parish storehouse and bell tower. No medieval timber was found inside the structure during a roof survey carried out in 2014, adding to the puzzle of its original purpose and exact age.
The church has had a succession of notable organs, including an instrument built by the renowned organ builder Cahman in 1736, later instruments from the 1890s, and the current organ, installed in 1969, which reused some material from its predecessors.