Unlike most major airports, Trenton Mercer Airport is relatively inaccessible by public transportation. Furthermore, its position in the relative outskirts of the suburbs makes it inaccessible to those considering walking.
The closest railway stations are the Trenton Train Station at the Trenton Transit Center which serves as a stop for NJ Transit, Amtrak and SEPTA service, along with the West Trenton train station which is the final stop for SEPTA service to and from Philadelphia. Taxi or rideshare service would be required to the airport.
There are a number of taxi and limo companies serving the airport. Taxi rates to and from Trenton Transit Center are approximately $35 and $8 to the West Trenton train station. For alternatives, you can try Lyft or Uber and get free credits for your first ride.