Investigators in Portsmouth said a frantic person approached an officer Wednesday shortly after midnight, seeking help for the toddler.
The girl was unconscious and having trouble breathing.
Police said the girl's father and another person drove her to the hospital before the officer arrived at the scene in the Ohio River city, about 90 miles east of Cincinnati.
Investigators found the girl's 26-year-old mother unresponsive inside an apartment nearby. They said she had suffered from a suspected heroin overdose.
Both mother and daughter were treated, and now both the girl's parents are charged with child endangerment.
Court records didn't list attorneys for either parent.
The Associated Press contributed to this report.
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