Two rivers split Lavaca County's drainage map

Eastern Lavaca County drains toward the Navidad River. Its East and West branches meet northwest of Oakland before the Navidad joins the wider Lavaca River basin. The county's center and west drain toward the Lavaca itself. That river enters from Gonzales County, passes Hallettsville, and continues toward Lavaca Bay.

Rain changes both upper rivers, but runoff is not their entire story. A U.S. Geological Survey study measured groundwater seepage adding low flow to the Lavaca farther downstream. Pecan and elm gather along county streams, so the drainage map is also a vegetation map.

The names hold older layers. Lavaca comes from the Spanish word for cow; Navidad refers to the Nativity. The Lavaca also marked the line between Stephen F. Austin's and Green DeWitt's empresario grants. Andrew Kent's 1830 land stood on DeWitt Colony's eastern edge along the river, and he traveled from there to Gonzales and Lavaca Bay to trade. Refugees probably started another settlement along the river in 1826, though its exact site is unknown and it was soon abandoned. Long before Lavaca County had settled borders, the water had already drawn a boundary.