William Rabb, one of Stephen F. Austin's Old Three Hundred colonists, the eldest son of Andrew and Mary (Scott) Rabb, was born on December 21, 1770, in Fayette County, Pennsylvania. He married Mary Smalley about 1789 and they eventually had four sons, Andrew, John, Thomas, and Ulysses, and a daughter, Rachel, who later married Joseph Newman. Rabb and his family left Pennsylvania about 1803. After a brief sojourn with relatives in Ohio, Rabb reached his destination near the Mississippi River in Indiana Territory (later Illinois Territory) in 1804. There he built and operated a large gristmill on Cahokia Creek near present-day Collinsville, Illinois. He also served as Madison county judge and in 1814 was elected to the legislature of Illinois Territory, where he served for two terms. In 1818 the Rabbs moved to Clear Creek settlement on the north side of the upper Red River in Arkansas Territory, in what is now Choctaw County, Oklahoma. From there, Rabb made an exploratory trip into Texas in 1819 and chose an area on the east side of the Colorado River as the site he wished to acquire. When the federal government ceded the land north of the Red River to the Choctaw Indians in 1820, Rabb moved his family south of the river to Jonesborough, an area now in Red River County, Texas. Although the Arkansas Territory authorities attempted to exercise civil jurisdiction over the Jonesborough settlers, the Rabbs were technically in Spanish territory. In 1821 Rabb wrote a letter to the Spanish governor in San Antonio de Béxar which stated, among other things, that he intended to settle soon on the Colorado River as a member of Austin's colony. When and where Rabb first became involved in the plan of Moses Austin and his son, Stephen, to establish a colony in Texas is uncertain. Since Rabb is believed to have been a longstanding acquaintance of the Austins, he probably was aware of their plan at an early date. Somewhere along the line they reached an agreement whereby Rabb would build a gristmill in the proposed colony to help supply the settlers in exchange for a sizable grant of land.
Rabb and his wife and two unmarried sons left Jonesborough and arrived at his site on the Colorado River in December 1821. Probably for security reasons plus availability of fresh water from springs, they initially settled on the high ground west of the river at a place Rabb called Indian Hill. Located a short distance above present-day La Grange in Fayette County, it was directly across the river from the rich bottom land that he had chosen on his exploratory trip in 1819. When Stephen F. Austin returned from a journey to Mexico City in 1823 with the news that the Mexican authorities had reconfirmed his colonization contract and would honor land titles in the colony, Rabb returned to Jonesborough to fetch the remaining members of his family. They arrived in December 1823, and for a while the entire family remained at Indian Hill. However, in early 1824, they moved downriver to the little settlement of Egypt in present-day Wharton County in order to escape Indian harassment.
Title to Rabb's land grant was signed by Stephen Austin and Commissioner Baron de Bastrop on July 19, 1824. It was one of the earliest and largest grants made in Austin's first colony and comprised a total of five square leagues, or one "hacienda," of about 22,000 acres. Two leagues of approximately 9,000 acres were located in the area near the Gulf of Mexico known as Bay Prairie in present-day Matagorda County. The other three leagues of over 13,000 acres comprised the land granted to Rabb as the result of his agreement to build a gristmill in the upper portion of the colony. Situated on the east side of the Colorado River in present-day Fayette County, it is the site Rabb chose in 1819 and is the tract known today as Rabb's Prairie. Although he soon left Egypt and returned to Rabb's Prairie to begin work on the mill, Rabb was forced to abandon the project on several occasions due to threats of Indian attack. In 1830 the ayuntamiento of San Felipe de Austin, the governing council of Austin's colony, reviewed Rabb's situation and reconfirmed his title. Also, because of delays caused by Indian harassment, it approved an additional eighteen months for him to finish construction of the mill. With the help of his sons, Rabb completed his mill in 1831. Some of the material used in its construction came from New Orleans, but it was the transportation and installation of two large grinding stones, or burrs, that proved to be an accomplishment of considerable ingenuity and determination. The mill stones, each weighing around a ton, had been imported from Scotland and off-loaded at Matagorda at the mouth of the Colorado River. The problem facing Rabb was how to move these two ponderous objects to his mill in Rabb's Prairie, a distance of about 100 miles. Driftwood rafts and shallow water made it impractical to float them upriver on a barge. His solution was to make an axle, attach the mill stones on the ends to serve as wheels, and use oxen to pull the resulting vehicle overland to his mill. Rabb lived to see his mill in operation but died later in 1831. His wife died a few months afterward. They are believed to be buried in an old abandoned cemetery on a hillside overlooking Rabb's Prairie.