Yes, where a product is grown can make a difference in its iodine content. Foods from the ocean are higher in iodine than plant foods. Where land was under the sea many, many years ago, iodine can be found naturally in the soil. The soil around the Great Lakes region is lower than other areas of the country. This USDA searchable database would be the best place to look for any nutrient, but I don’t see that iodine is included, possibly because the iodine content will vary depending on where the food is grown. I am not familiar with studies on iodine content of potatoes. You might want to try eating plants from the sea, seaweed or kelp, as another possible source of iodine. Finally, goitrogens in the diet can inhibit iodide metabolism. Goitrogens can be found in raw turnips, cabbage, Brussels sprouts, cauliflower, broccoli, rutabagas, and cassava but can goitrogens can be reduced by cooking these vegetables. You might want to talk to your doctor and check your thyroid levels; we don’t typically hear about a lot of goiter (iodide deficiency) in the US.