When Union Township was organized in 1819, it became the third township in the county. From the onset, it assumed its present boundaries of "all the county bounded on the north by the 'big bayou' (Bayou Creek) and on the other side by the Ohio River"
Surrounded on three sides by the river, Union Township was prone to flooding, but that left the soil as rich farmland. Settlers in the area date back as early as 1806, though farmsteads were quite a distance from each other. When the 1937 Flood occurred, it wreaked havoc on the township. The entire area was underwater, and several homes that were damaged or destroyed were never rebuilt.