Regions are tricky business. According to About.com's guide to Geography, states don't technically have regions assigned to them. For example, the geography guide notes:
"You could call Oregon a Pacific state and a Northwestern state (although the term Pacific Northwest is frequently also used.)"
That said, when discussing certified organic crops or farms in specific regions, it's a little up to personal interpretation.
Even the USDA is a tad unclear. For example, the USDA offers an easy to access chart of USDA production regions for the 48 contiguous states, but Alaska, Hawaii, Puerto Rico and the Pacific Basin are not included in this chart. In another breath, the USDA notes that there are indeed 10 major farm production regions in the United States, but that Alaska and Hawaii are included with the Pacific region.
Other various regional charts offered by the USDA that fall under the Farm Resource Regions include: