The longtime area resident sustained only minor injuries, responders said.
She'd complained of head and back pain, Detective Travis Woods said.
It was initially unclear why the well on Trinity Place, near the corner of Liberty Avenue, wasn't covered.
Members of the Urban Area Security Initiative (UASI) team got the woman out safely.
The team included responders from the Hackensack, Woodcliff Lake and Paterson fire departments and North Hudson Regional Rescue.
Borough police also requested an Advanced Life Support unit as a precaution after the woman fell into the well around 10:45 a.m.
ALL PHOTOS: HILLSDALE FIRE DEPT.
Click here to follow Daily Voice Northern Valley and receive free news updates.