 The river begins on the northern border of Liberty County, forming the San Jacinto - Polk County line through the Liberty County line.The east fork of the San Jacinto River flows through far northeast parts of the county, flowing through Cleveland.Tarkington Bayou begins in the Sam Houston National Forest in San Jacinto County, working its way south through northeast and east Liberty County and joining other feeders, before traveling into Harris County and emptying into Galveston Bay.