By 1803, when the United States acquired Louisiana, the area of Jefferson County was under Spanish control as part of the Atascosito District. In 1821 filibustering efforts ceased when the Treaty of Córdova ended Spanish ownership in the region and made it part of Mexico. The first settlement within the confines of the present county, made at Tevis Bluff in 1824, became Beaumont. The area that became Jefferson County was included in the Mexican Department of Nacogdoches as part of Liberty Municipality in Lorenzo de Zavala'sqv empresarioqv grant of 1831. It later became part of Jefferson Municipality. The Cow Bayou settlement in this municipality, organized in 1835 and later known as Old Jefferson, became the first county seat and the place through which the county grew. Jefferson County, formed in 1836 and organized in 1837, was one of the original counties in the Republic of Texas.qv It was named for the municipality that preceded it, which was in turn named for Thomas Jefferson. The county boundaries, as delineated on December 21, 1837, included all of the future Orange County, a part of what later became Hardin County, and the extreme eastern part of the future Chambers County. The first county seat, Jefferson, or Old Jefferson, on the east bank of Cow Bayou, was replaced by Beaumont in 1838 and had disappeared by 1845, when the site of Orange was surveyed. Orange was first called Jefferson or New Jefferson. -Handbook of Texas Online: Jefferson County