Oso was an unincorporated rural community located on the divide between Haw and Rocky creeks three miles northeast of Flatonia in southwestern Fayette County. Like that of many small rural communities in the area, the population was predominantly Anglo American in the beginning with family names such as Menefee, Lane, Harrison, and Cobb; subsequently waves of immigrants from central and eastern Europe settled in the area. Small farms produced cotton on moderately deep and loamy topsoils. A post office was established in 1858, and Oso became the center of a voting precinct with three stores, a mill, a gin, a tannery, and a blacksmith shop. In 1874 the Galveston, Harrisburg and San Antonio Railway extended its line through Flatonia, and all business interests moved there. The post office closed in 1874, and by 1900 only the place name remained.