Drainage & Water
Parker County drains into two different river systems
The western part of the county flows into the Brazos River, while the eastern part drains toward the Trinity River.
Parker County sits on a divide between two major Texas river systems. Rain in the west drains toward the Brazos River. Rain in the east drains toward Trinity River tributaries. That split matters for flood risk, water rights, and which river authority has jurisdiction on your land.
Both the Brazos River Authority and Trinity River Authority can have roles in managing water and reservoirs in the area. If you own land near a creek or low area, knowing which watershed you are in helps you understand your flood map zone and who regulates nearby water. Start with FEMA's flood map viewer at msc.fema.gov, then check with the relevant river authority for local rules.
Source to confirm: TSHA Handbook — Parker County