Optimizing nitrogen (N) fertilization is important to improve corn yield and to reduce N losses to the environment. The economic optimum nitrogen rate  (EONR) is variable and depends on many factors, including weather conditions and crop management.  The main objective of this study was to examine how grain corn yield response to N varies with planting date, soil texture and spring weather across sites and years in Monteregie, which is the most important with 64% of total area and 69% of total harvested grain for this crop in Quebec province. This experiment was conducted during 8 years (2002 to 2004 and 2006 to 2010), at 11 sites with 23 hybrids and four N applications rates, for a total of 45 site-years. Each six year involved five and six rates ranging from 80-90 to 240 kg N ha-1.  Trials were separated into two groups based on optimal and late planting dates. Grain yield response to N varied among site-years. Significant differences in grain yield among the applied N rates were observed in all of the site-years planted at optimal dates (from 8.8 to 14.7 Mg ha-1), and in most of those planted late (8.5 to 12.8 Mg ha-1). Overall, optimal planting window increased grain yield compared to late planting. EONR ranged less widely for site-years planted on optimal dates (180 to 237 kg N ha-1) than for those planted late (132 to 237 kg N ha-1). Soil textural classes and rainfall affected the EONR.  The average EONR was 193 and 204 kg N ha-1for fine-textured soil and coarse-textured soil, respectively.  Response to fertilizer N was higher for early planted corn combined with wet conditions. These results suggest that the current N guideline may need to increase for the optimal planting window and should be based on soil texture and weather.