On a 1997 Buick Regal, the starter is located on the
passenger side (right side) of the engine, generally towards the bottom. You'll likely need to access it from underneath the car. It's usually bolted to the engine block near the transmission bellhousing.
Because there are different engine options for the '97 Regal (and slight variations even within those engines), precise location can vary slightly. A repair manual specific to your engine is the best resource for exact placement.
