Margaret Leatherbury (Letherbury, Leatherberry) Hallett was born on December 25, 1787, in Stafford County, Virginia. At the age of eighteen she fell in love with John Hallett, an English-born merchant seaman, whom her well-to-do family considered an unsuitable match. In 1808 she left home and joined him in Baltimore. They were married aboard ship in Chesapeake Bay and lived in Baltimore for several years before moving west. Their first two sons were born in 1813 and 1815 in Matamoros, Tamaulipas, where the Halletts operated a store until it was confiscated by the Mexican government. They then moved to Goliad, Texas, and set up a trading post. There a third son was born in 1818 and a daughter in 1822.
The Halletts were still living in Goliad in 1833, when John took a league of land in Stephen F. Austin's colony on the east bank of the Lavaca River in what is now Lavaca County. He brought workers and building materials from Goliad to construct a cabin, but not long after it was completed he died and was buried in Goliad. After the Runaway Scrape Margaret and her daughter, her only surviving child, moved onto the Hallett league. Margaret turned the cabin into a store and traded for pelts and hides with the Tonkawa Indians and the White settlers, who were beginning to fill up the area; she then had the hides carted to Gonzales and exchanged for corn. She had a field cleared for a crop, raised horses under her own brand, and acquired a basic vocabulary in Tonkawa. Legend credits her with raising a lump on the head of a Tonkawa who attempted to help himself to merchandise. Chief Lolo is said to have rewarded her with the nickname Brave Squaw and with honorary tribal membership.
In 1838 Margaret Hallett donated land adjoining her trading post for a townsite, which was named Hallettsville in her honor. She built a new home there and promoted the town vigorously. In 1842 the legislature authorized the establishment of a judicial county to be named La Baca, which later became Lavaca County. County and district court sessions were held in the Hallett home pending the selection of a county seat. Hallettsville and the older town of Petersburg were contesting for the honor; some sources report that Margaret Hallett was instrumental in having the county records moved from Petersburg to Hallettsville in the early 1850s and seeing that they remained there. In 1852 she gave the building site for Alma Male and Female Institute and helped organize the new institution. She died in 1863 and was buried on the Hallett league. Later her remains were transferred to City Memorial Park, where a grave marker acknowledges her as the founder of Hallettsville.