The Centers for Disease Control and Prevention confirmed a patient was infected in Dallas County, health officials in Texas said.
A patient was apparently infected after having sexual contact with someone who returned from a country where the disease is present.
There is not yet evidence of Zika being passed on by mosquitoes in the US.
This would be the first known infection to take place in the mainland US.
The World Health Organization has declared the Zika virus a global public health emergency.