An inbred maize line, designated PH91C, the plants and seeds of inbred maize line PH91C, methods for producing a maize plant, either inbred or hybrid, produced by crossing the inbred maize line PH91C with another maize plant, and hybrid maize seeds and plants produced by crossing the inbred line PH91C with another maize line or plant and to methods for producing a maize plant containing in its genetic material one or more transgenes and to the transgenic maize plants produced by that method. This invention also relates to inbred maize lines derived from inbred maize line PH91C, to methods for producing other inbred maize lines derived from inbred maize line PH91C and to the inbred maize lines derived by the use of those methods.