I bought ginger root months ago, and I didn't use all of it. I've kept it in the fridge and it still seems good. How long will it last?
Eat By Date claims a shelf life of about one month, in the refrigerator, which matches my experience.
Ginger root is a living rhizome, and is the plant's way of storing energy to grow later. As long as it is firm, not slimy, with no signs of a mold, with a good aroma, you should be able to use it.
You could store it in the freezer for a few months longer (about 3 or so) the next time you pick some up. Since I typically grate it, I haven't noticed any texture issues. Otherwise, I find it lasts 4-6 weeks normally in the fridge.