Layne Hardin says Texas Andrology Services handed over the vials to Toby Devall without his permission.
Mr Hardin’s lawyer said Ms Devall had “bluffed” her way to getting the sperm before being inseminated at a fertility clinic. The clinic has not commented.
The child is now two years old and Mr Hardin may have to pay child support.
He told local TV he wanted “to throw up, cry, pass out” after finding out.
The case is not the first of its kind. In 2011, Joe Pressil of Texas sued his ex-girlfriend and a fertility clinic, claiming she used his sperm to get pregnant without his permission.