A jailer gave candy and treats to a 15-year-old being held in the Harris County Juvenile Justice Center in exchange for sex, prosecutors said.
Robert Emerson Robinson, 28, has been charged with sexual abuse of a child.
Houston police said the incident happened in May.
Detectives said Robinson admitted to having sex with the girl in her cell at the facility at 1200 Congress.
There is surveillance video of Robinson going into the girl's cell while the lights were off, police said.
"Absent that video camera, would anyone have ever believed this juvenile inmate?" KPRC Local 2 legal analyst Brian Wice asked. "I think that's what makes these alleged predators so dangerous, because they rely on the notion that people in custody don't make credible witnesses."
Officials with the Harris County Juvenile Probation Department said Robinson's employment was terminated in August, shortly after they learned about the incident. He had been with the department for six years.
Robinson was booked into the Harris County Jail and released after posting $30,000 bond.