County Origins
Washington County Was One of the First Counties in Texas
Washington County was established by the Republic of Texas in 1836, the same year Texas declared independence.
The Republic of Texas established Washington County in 1836 and organized it in 1837. Stephen F. Austin's colonists had been settling the area since 1821. Washington-on-the-Brazos sat at a Brazos River ferry crossing. It was the county's first community. It served as the Texas Republic's capital in the early 1840s.
Brenham became the county seat in 1844. In 1858, Washington-on-the-Brazos residents refused to pay an $11,000 bonus to attract the Houston and Texas Central Railway. They wanted to protect their river trade. The railroad went to Navasota instead. Washington-on-the-Brazos quickly declined after that. Brenham grew into the regional center it is today.
Source to confirm: TSHA Handbook – Washington County