The economic viability of using summer-seeded legume cover crops (crimson clover, red clover, and hairy vetch) as a primary nitrogen (N) source for an organic corn (Zea mays L.)–soybean (Glycine max (L.) Merr.)–winter wheat (Triticum aestivum L.) rotation was determined on a sandy loam soil in southwestern Ontario, Canada, by comparing gross profit for organic production (organic sources of N and phosphorus, no herbicides) to conventional production (no cover crops, synthetic fertilizers and herbicides added). Profits were determined for the initial 3-year transition period from conventional to organic production (2015–2017), and for 5 years of certified organic production (2018–2022). During the transition period when conventional crop prices applied to both production systems, organic production profits (CAD $1148–$1869 ha⁻¹ per rotation) were lower than conventional profits (CAD $2126 ha⁻¹ per rotation). During the certified organic period when price premiums were applied, organic soybean and corn profits (CAD $1995–$2274 ha⁻¹ and $2819–$3195 ha⁻¹ per year, respectively) were significantly greater than conventional soybean and corn profits (CAD $536 ha⁻¹ and $1926 per ha⁻¹, respectively). Winter wheat profits were slightly higher for organic production (CAD $426–$825 ha⁻¹ per year) than for conventional production (CAD $371 ha⁻¹ per year). During the certified organic production period, profits from the 3-year rotations were CAD $5533–$6153 ha⁻¹ for organic production, and CAD $2860 ha⁻¹ for conventional production. It was concluded that an organic rotation of corn–soybean–winter wheat/legume cover crop can be economically viable and more profitable than conventional production on sandy loam soil in southwestern Ontario.