A lemon can usually stay a week on your countertop or three weeks in the crisper before it spoils, but if you wish to keep lemons fresh for longer, consider freezing them.
Toss away any that show signs of mold or bruising. Make sure your lemons are clean and dry, so rinse or brush them if necessary, then pat them completely dry with a paper towel.
Next, wrap each fruit in plastic food wrap, or if you want to keep them all together, use a ziplock bag — just be sure to squeeze out as much air as possible before sealing it.