254 of 254 Harris County Courthouse, Houston, Texas. Population: 4,680,609. The largest in Texas.

"Harris County, originally Harrisburg County, is located on the upper Gulf Coast in Southeast Texas and is bounded by Waller County on the north and west, Montgomery County on the north, Liberty and Chambers counties on the east, Galveston and Brazoria counties on the south, and Fort Bend County on the west.
"The county comprises 1,778 square miles (1,729 in land) and is the largest Texas county east of the Nueces River. Its southern half is level coastal prairie, and the northern half touches the rolling East Texas timberlands. Central Harris County is fifty-five feet above sea level. The land rises gradually to more than 200 feet on the northern borders, while the smallish bluffs around upper Galveston Bay descend to sea level.
"In 1826, John R. Harris laid out Harrisburg on his league where Brays Bayou joined Buffalo Bayou, the head of navigation. He opened a store and built a saw and grist mill, while his brothers captained vessels between there and New Orleans and even Tampico.
"Harrisburg County was formed by the First Congress on December 22, 1836. The lawmakers also named Andrew Briscoe chief justice and the infant city of Houston the county seat and national capital. The county encompassed the territory of the old municipality plus Galveston Island (the mainland was attached to Brazoria County) until May 1838, when its modern boundaries were established. In December 1839, Congress changed the name to Harris County, in honor of John R. Harris."
Handbook of Texas Online, Margaret Swett Henson
"The county comprises 1,778 square miles (1,729 in land) and is the largest Texas county east of the Nueces River. Its southern half is level coastal prairie, and the northern half touches the rolling East Texas timberlands. Central Harris County is fifty-five feet above sea level. The land rises gradually to more than 200 feet on the northern borders, while the smallish bluffs around upper Galveston Bay descend to sea level.
"In 1826, John R. Harris laid out Harrisburg on his league where Brays Bayou joined Buffalo Bayou, the head of navigation. He opened a store and built a saw and grist mill, while his brothers captained vessels between there and New Orleans and even Tampico.
"Harrisburg County was formed by the First Congress on December 22, 1836. The lawmakers also named Andrew Briscoe chief justice and the infant city of Houston the county seat and national capital. The county encompassed the territory of the old municipality plus Galveston Island (the mainland was attached to Brazoria County) until May 1838, when its modern boundaries were established. In December 1839, Congress changed the name to Harris County, in honor of John R. Harris."
Handbook of Texas Online, Margaret Swett Henson