Illustrative embodiments of diaphragm pumps including a muffler-mounted sensor are disclosed. In one illustrative embodiment, a diaphragm pump includes a shaft coupled to at least one diaphragm, an exhaust chamber configured to receive a motive fluid that has driven reciprocation of the at least one diaphragm and the shaft, a muffler disposed at least partially within the exhaust chamber, the muffler having a sensor mounting chamber defined therein, and a proximity sensor disposed in the sensor mounting chamber, a sensing end of the proximity sensor being flush with an end of the sensor mounting chamber nearest the shaft.