The Everstone is a held item in Pokemon Sword and Shield that prevents a Pokemon from evolving while holding it. It also is an important Pokemon Breeding item, and is needed to solve a ruin riddle in The Crown Tundra. This page covers how to find an Everstone.
How to Get an Everstone
You can find an Everstone in Turrfield in front of the Pokemon Gym in that town – see the screenshot below.
You can find additional Everstones via the Digging Duo in the Wild Area, and sometimes Pokemon bring them back with them after going on a Poke Job. You can find two more Everstone in The Crown Tundra: check for items in the Roaring-Sea Caves, and on the left side of the river bank at the Giant’s Foot. There is also an Everstone on Challenge Road at the top in the Isle of Armor.
Before doing that, you may have a Pokemon holding it in your box, so search for it in your boxes as well! Everstone is a common Breeding item too, so check Pokemon left at the Daycare Center, as you may have forgotten it!