The evolution of maize as an organism, its spread as an agricultural crop, and the evolution of Native American maize-based agricultural systems are topics of research throughout the Western Hemisphere. Maize was adopted in Northern Iroquoia, comprising portions of present-day New York, Ontario, and Qu\ ebec by 300 BC. By the fourteenth-century AD, maize accounted for \>50 to \>70\% of ancestral Iroquoian diets. Was this major commitment to maize agriculture a gradual incremental evolution, or was there a rapid increase in commitment to maize-based agriculture around AD 1000 as traditional archaeological narratives suggest? Summed probability distributions of direct radiocarbon dates on maize macrobotanical remains and cooking residues containing maize phytoliths combined with maize macrobotanical maize densities at sites and previously published stable isotope values on human bone collagen used with Bayesian dietary mixing models and cooking residues show an initial increase in maize use at AD 1200–1250 and a subsequent increase at AD 1400–1450. These results indicate maize history in Northern Iroquoia followed an exponential growth curve, consistent with Rindos’ (1984) model of agricultural evolution.