Brazoria County created 3/17/1836, organized 1837
Brazoria County became part of the Victoria district when Austin's original San Felipe district was divided in two in 1826. In 1832 the legislature of Coahuila separated Brazoria Municipality from San Felipe and made Brazoria its capital. A decision was made to change the name of the municipality from Brazoria to Columbia, to make Columbia the seat of government, and transfer some territory to Matagorda Municipality.
After his capture at the battle of San Jacinto on April 21, 1836, Santa Anna and members of his army were taken to Velasco, then the location of the provisional government. Here Santa Anna signed the Treaties of Velasco with the Republic of Texas on May 14, 1836. Columbia, the seat of the ad interim government, served as the capital of the republic when sessions of the first Texas Congress met in October 1836. During the first session Stephen F. Austin died and was buried at Peach Point. Houston became the capital.
Under the provisional government, Texas accepted the constitution that made its first counties from former municipalities. Brazoria County, among the first, took its name from the Brazos River when the Congress of the republic established it on March 24, 1836. Brazoria, which became county seat when the county was organized on December 20, 1836, served until 1896, when Angleton replaced it. The establishment of Fort Bend County in 1837 and of Galveston County in 1838 drew the present county boundaries, and the towns of Columbia, Velasco, and Brazoria were incorporated by the Congress of the republic in 1837. -Handbook of Texas Online: Brazoria County