Historically, fire disturbance played a major ecological role in the structure and function of many forested ecosystems of the upper Midwest. Human activity patterns have since disrupted the historic fire regimes following human settlement. However, the spatial pattern of human influence on current fire regimes is not well understood. We evaluated the relative importance of human influence on fire ignitions and fire size at two spatial resolutions in a 75,000 square km region of northern Wisconsin using a 16-year fire record database. Classification and regression tree (CART) analysis indicated that fire ignitions were most associated with two correlated variables: human population and housing density. Other important factors included those that affected human access to natural vegetation (e.g., distance to roads or railroads). Increasing the minimum fire size threshold increased the relative importance of ecological variables, including land type associations ranked according to their historic fire rotations, as well as the proportion of agricultural or grassland cover types. Collectively, our results suggest that while human factors dominate the probability of fire ignitions, ecological factors constrain the ability of those fires to spread. These results have strong implications for forest dynamics and fire risk at the human-wildland interface in the upper Midwest.