Old Ocean is on State highways 35 and 524 five miles northwest of Sweeny in southwestern Brazoria County. The site was located on or near the land grant patented by Joseph H. Polley and Samuel Chance on July 27, 1824, and became known as Chance's Prairie, a name that has survived to the present. Original patentees in the vicinity of Old Ocean Lake (later Old Ocean Swamp), three miles to the south, included Mills M. Battle, M. Berry, Thomas H. Borden, Charles Breen, Benjamin C. Franklin, Freeman George, Henry W. Johnson, Oliver Jones, Imla Keep, David McCormick, Zeno Philips, Thomas Walker, John Williams, and Robert Harris Williams. William B. Sweeny, one of the early settlers on Chance's Prairie, arrived in Brazoria County in 1832. His father, mother, two sisters, six brothers, and their slaves, reportedly numbering 250, arrived the next year and settled on the Breen league, along the southern boundary of Polley and Chance's land. On March 25, 1835, Polley and Chance sold 2,319 acres to Sweeny for $1,950. Eventually the six surviving children of John Sweeny, Sr., who died in 1854, owned adjoining plantations in the area. Others living on Chance's Prairie before the Civil War included Sampson Brown, a slave born in Maryland and bought by Joseph McCormick in 1837. After emancipation Brown traveled a circuit in Milam and Fort Bend counties as a teacher and preacher. Prince Monroe, another slave belonging to Joseph McCormick, managed McCormick's plantation for the better part of twenty years. After the war the post office for Chance's Prairie was located in the commissary on John Sweeny's plantation. Chance's Prairie had a reported population of eighteen in 1880. Around 1906 the area had four schools for black children and employed four teachers; the combined enrollment was 199. James (Jim) Abercrombie discovered oil nearby in 1934, and a government oil refinery was constructed to make high-octane gas. It was closed at the end of World War II. The oilfield was named Old Ocean, and by 1936 the name of the community had been changed to Old Ocean. The 1936 county highway map shows a nearby school, the Bethlehem Church a mile west on State Highway 35, and numerous buildings and dwellings at the site. The community had a post office by 1945 and a population of 800 and four businesses in 1947. Old Ocean had 1,000 residents and nine businesses in 1964 and 900 residents and eight businesses in 1972. In 1974 the community had two churches. The population was reported as 915 from the 1970s through 2000. Nineteen local businesses were in operation in 1982 and eight in 1992. By 2000 the number of businesses had increased to twenty-one.