Technical Abstract: Ammonia (NH3) emissions were determined from three commercial dairy farms in the north-central United States. The dairies employed similar management, having naturally-ventilated free-stall barns where barn waste is scrapped and transferred to outdoor lagoons. Three potential emission components were distinguished at each farm: barns, lagoons, and sand separators. A backward Lagrangian stochastic (bLS) inverse-dispersion technique was used to measure emissions. Total farm emission rates varied from 15 to 330 kg NH3 d-1, depending on the farm and season. The inter-farm variability was largely explained by farm size (animal population). Emissions showed variability on seasonal and daily scales: summertime rates were roughly ten times those of the winter, and mid-day rates were approximately three times those at night. Lagoons were the largest emitter during summer and fall, representing 50 to 63% of the farm total (lagoons were frozen in winter and emissions were immeasurably small). On a per-animal basis, the yearly average emission rates from the three dairies were estimated to be 55, 51, and 55 g-NH3 animal-1 d-1. Regarding the measurement technique, bLS proved well-suited to our study. With modest resources we were able to measure emissions from the variety of sources at each farm, and quickly move between farms. Overall agreement in measured emissions at the three farms, together with a general harmony of our measurements with those from previous studies, provides a measure of confidence in the measurement strategy.