The accused, also a Dalit, was known to the girl's family and visited her home often, SP Alankrita Singh told PTI from Hapur over phone.
The girl has identified the youth who has confessed, Singh said.
The girl's clothes have also been recovered from him, she said, adding a medical examination of the girl confirmed rape.
The accused will be produced before a juvenile court today, Singh said.
Meanwhile, a three-member team of doctors is attending to the victim at a hospital here. Gynaecologist professor Kirti Dubey said the girl is running a minor fever and will be fine in 1-2 days.
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The girl was later found unconscious and naked near a tubewell in a forest near the house. Angered by the incident, villagers had blocked the NH-24 on Saturday.
The Uttar Pradesh Government has come under flak over a string of rape incidents, including the gangrape of a woman and her daughter who were dragged out of their car by the accused on National Highway-91 in Bulandshahr.