Crop rotation can significantly affect N use by corn (Zea mays L.), suggesting that residual soil NO₃-N following corn may differ among crop rotations. The effect of N rate on fall residual NO₃-N to a depth of 91 cm was tested in continuous corn (CC) and corn-soybean [Glycine max (L.) Merr.] (CS) crop rotations at seven locations in Illinois from 2000 to 2003. Across locations, total residual NO₃-N values following a corn crop grown without fertilizer N in CC and CS were 20.4 and 21.3 kg ha^-1, respectively, while following 252 kg N ha^-1 these values were 89.7 and 83.7 kg ha^-1. The response of residual NO₃-N to N rate did not differ between rotations when averaged across all locations, though across N rates at Monmouth, residual NO₃-N was 16% greater in the CS rotation compared to CC. Residual NO₃-N increased linearly with N rate at six locations, but the response was quadratic at Perry. In the CS rotation in the low organic matter soil at Brownstown, residual NO₃-N was higher when corn yields were higher without fertilizer N, suggesting that soil N supply exceeded N uptake. In the low organic matter soil at the upland site at Dixon Springs, higher optimum N rates in CC were associated with higher residual NO₃-N at that N rate after harvest. As N rate for maximum yield increased, residual NO₃-N after harvest at that N rate increased with the CS rotation at Monmouth and decreased with the CC rotation at Perry. Overall, neither crop rotation nor optimum N rate had consistent effects on residual NO₃-N. It is clear that residual soil NO₃-N levels are the consequence of complex interactions among soil, crop, and weather, such that predicting such levels following crops will be difficult.