These are not accepted at curbside. Instead take them back to the grocer. They should have a plastic bag recycling container usually located in the entrance way or customer service area.
Store specific info:
Price Chopper on Rt 9 Shrewsbury -> bin is located in the walk way past the outer doors.
Stop & Shop on Rt 9 Shrewsbury -> a bin is located in each of the vestibules
Target Lincoln Plaza Worcester -> bin located in the waiting area at Customer Service