Oldenburg was first settled in 1817 by William George of Pennsylvania. J. Henry Ronnebaum and Henry Plaspohl platted the town in 1837 and named it for the Dukedom of Oldenburg in Germany, from whence they came. The first church and school were built in 1837, the first post office was erected in 1845, and the town was incorporated in 1869 with Ben Flodder as president of the Town Board. The cornerstone of Town Hall was laid on Washington's Birthday in 1878.