Police said the girl's mother found the note when she returned to the family's residence Monday afternoon.
The note indicated the girl was heading to the New Jersey Transit train tracks with the intention of ending her life, police said.
Township police said they notified Chatham Borough, Summit, Madison and New Jersey Transit to look for the girl, and township and Summit police walked the train tracks to search for her.
One NJ Transit conductor saw an individual along the tracks matching the girl's description, police said.
The Morris County K-9 unit was brought in and helped locate the girl in the wooded area near the Passaic River and River Road, according to police.
The girl told police she had taken pills, and a township officer transported the mother to the scene, police said.
The Chatham Emergency Squad transported the girl to Overlook Hospital where she was kept overnight, according to police.
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