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Canopy reflectance sensing can be used to assess in-season crop nitrogen (N) health for subsequent control of N fertilization. The several sensor systems that are now commercially available have design and operational differences, including sensed wavelengths, size of the sensed area, and nadir vs. oblique sensing orientation. Data comparing the different sensor designs is lacking. Thus, the objective of this research was to evaluate three different commercial canopy reflectance sensors for N fertilization control in corn. Two units of each of three commercial sensors GreenSeeker, Crop Circle, and CropSpec were mounted to a high-clearance applicator for field data collection. Data were collected multiple times on plots with eight different N rates 0 to 235 kg N ha-1. Relative NDVI data from GreenSeeker and Crop Circle sensors were most highly correlated, while data from those two sensors were less strongly related to CropSpec data. CropSpec NDVI was more strongly related to SPAD readings as an indication of leaf N, while the other two sensors were more affected by crop height variations. For multiple data collection runs in a single day, somewhat less run-to-run variation was seen with the CropSpec. For best results, users need to take into account the differences among these commercial sensors, particularly between the two small-footprint nadir sensors (Crop Circle and GreenSeeker) and the large-footprint, oblique sensor (CropSpec).