Technical Abstract: U.S. organic dairy production has increased to meet demand for organic milk. Organic dairy farmers have come under increasing financial stress due to increases in concentrated feed prices. Organic dairies in the Northeast U.S. have experimented with different forage and grain crops to maximize on-farm production of protein and energy to improve profitability. Three representative organic feed systems were modeled using the Integrated Farm System Model(IFSM)for farms with 30, 120, and 220 milk cows. Increasing intensity of equipment use was modeled ranging from organic dairy farms growing only perennial sod (Low) to those with corn-based forage systems which purchase supplemental grain(Medium)or which produce and feed soybeans(High). The profitability of the feed systems was strongly dependent on farm size. Results suggest smaller organic dairies can be more profitable with perennial sod-based feed systems due to lower fixed costs associated with less machinery. The largest size was more profitable using a corn-based system due to greater economies of scale in feed production. The intermediate farm size of 120 cows with corn-based forage systems were more profitable if perennial sod crop harvest was delayed. Delayed harvest decreased the protein and energy content of perennial sod crops requiring more purchased grain to balance the ration and resulting in lower profits. Corn-based systems were less affected by lower perennial forage quality since silage corn is part of the forage base. Large corn-based organic dairy farms that produced and fed soybeans minimized off-farm grain purchases and were the most profitable at the largest farm size modeled.