The Washington County Courthouse in Brenham, Texas, United States. The Courthouse was designated a Recorded Texas Historic Landmark in 1985 and listed on the National Register of Historic Places on March 29, 1990. – Larry D. Moore, CC BY 4.0 – Wikimedia Commons Washington County is located in Texas. About 34,765 people live here. Between 2010 and 2020, the population grew from 33,718 to 35,805. The area covers about 1,609.0 square kilometers. The region is divided into 2 Municipalities. The region was founded in 1836. The name originates from George Washington (Founding Father and first U.S. president) Washington County is county in Texas, United States. More information at www.co.washington.tx.us.