[1] Its county seat is Brenham, which is located along U.S. Highway 290, 72 miles northwest of Houston.

Washington-on-the-Brazos in the county is notable as the site of the signing of the Texas Declaration of Independence during the Convention of 1836.

Harry Haynes said, "This grand old county, the birthplace and cradle of Texas liberty, is in a sense a vast town cemetery.

Gilead, Rock Island, Jacksonville, Mustang, all by the inexorable decrees of new conditions and changes wrought in the course of human events have been blotted from the face of this beautiful earth.

"[11] Since the 1940s, Washington County has been powerfully Republican, with the only Democratic presidential candidate to carry it since Franklin D. Roosevelt’s 1936 landslide being Hill Country native Lyndon B. Johnson in 1964.

Washington was one of 11 Texas counties to vote in 1920 for American Party candidate James E. Ferguson, and the solitary county to give a majority to the conservative “Texas Regulars”, which were a predecessor to the numerous “Dixiecrat” movements of the following two decades, in the 1944 election.

[23] Additionally, Washington County is the sole taxation zone for Blinn College, meaning it is the only place with in-district tuition.