Denton County reported its first case of Zika virus on Tuesday.
Officials said the woman traveled internationally to a Zika-prone area in late January. No other details about the woman were given.
The total number of Zika cases in Dallas County is five. Tarrant County has three cases.
Scientists increasingly believe the Zika virus sweeping through Latin America and the Caribbean causes devastating defects in fetal brains if women become infected during pregnancy.