Waterloo is on Pecan Creek and Farm Road 619, four miles northeast of Taylor in eastern Williamson County. Though there were settlers in the area by the 1880s, the community really took shape after Josiah W. Rainwater built a store on the site about 1890. When a post office was opened in 1893, the office and the community were named Waterloo, after Rainwater's hometown in Kentucky. At different times in the 1890s the community had two churches, a gin, a drugstore, and a blacksmith shop. The Waterloo school was the eighth largest district school in Williamson County in 1903. Waterloo declined in the early decades of the twentieth century, losing its post office in 1904 and shrinking to a population of ten in 1933. Though the Waterloo school was consolidated with that of Thrall in 1949, the community revived somewhat in the 1940s, and had an estimated population of sixty in 1949 through 2000.