Subsurface tile drainage is an important water management practice on naturally poorly-drained soils, and recommendations for appropriate drain spacings for particular soils continue to evolve. The objective of this 20-yr study was to measure corn (Zea mays L.) and soybean (Glycine max L.) growth and yield as affected by subsurface drain spacing on a soil that was traditionally not tile drained. Three drain spacings (5, 10, and 20m) were compared with an undrained “control” (40m) on a low organic matter silt loam soil. The first 10 years included monoculture corn and chisel tillage while years 11 to 20 consisted of a soybean-corn rotation and no-tillage. Corn populations, heights at 4 and 8 weeks, yield, and grain moisture content were measured with distance from the drain for the 5-, 10-, and 20-m spacings. Significant distance effects occurred more frequently for the 20-m spacing than for the 10- and 5-m spacings, especially for yield and grain moisture content values. The 10-y average monoculture corn yields were not significantly different among treatments, being 9.8, 9.7, 9.5, and 9.2 Mg/ha for the 5-, 10-, 20-, and 40-m (control) plots, respectively. Significantly lower yields for the control plots in three of the 10 years were likely the result of both planting date delays and wetter soil conditions after planting. In the soybean-corn rotation, corn yields were significantly lower in the control plots than in the drained treatments in three of the five corn years, with 5-y averages of 9.0, 8.9, 9.0, and 7.9 Mg/ha for the 5-, 10-, 20-, and 40-m (control) plots, respectively. Extremely wet early-season weather in the last year of the 20-y study contributed to the lowest corn yields measured during the study. The results underscore that drainage improvements are a long-term investment and may not provide yield benefit in every year.