State Police spokesman Steven Jones said the system was activated around 1 p.m. Wednesday for a 75-year-old woman with Alzheimer's disease.
The woman, whose identity was not released, left home in her car Wednesday morning and did not return.
With the alert issued, the Department of Transportation activated electronic signs on major highways with the vehicle description and license number.
A motorist spotted the car on the Garden State Parkway in Bergen County at about 8 p.m.
Police responded and took the woman to a hospital to be checked out.
New Jersey passed its law creating the Silver Alert system last December.