The town was platted in 1837 by two German speculators who named the new town in honor of their home, the province of Oldenburg in Northern Germany. German Catholics coming from Cincinnati erected the first church, a log building, in 1837. Father Franz Joseph Rudolph was appointed Pastor of Oldenburg in 1844. He, in turn, invited Mother Teresa Hackelmeier to establish the Convent in 1851. From this background evolved the Catholic triad of Holy Family Church, the Franciscan Monastery, and Immaculate Conception Convent and Academy. Unfortunately, the Monastery was recently closed.
The most distinctive architectural aspect of Oldenburg is, of course, its many spires. Another significant aspect is the fact that 80 of the roughly 115 homes in the historic district were constructed prior to 1900. The oldest structures are constructed of stone or wood or a combination thereof. Brick structures were not built until after 1858 with bricks from the Gehring Brickyard at the south edge of town. The use of cast and wrought iron as well as the unusual work of master tinsmith Casper Gaupel provide the community with great visual richness. Many of the buildings in the community follow the Old World tradition of combining shop and residence under one roof.
The town of Oldenburg was listed on the National Register of Historic Places in March, 1983.