Mimics seem to spawn more frequently in the Underground Corruption, Lihzahrd Temple, Underground Crimson, and Underground Hallow. This is because a smaller variety of monsters can spawn in these biomes.

How do you get mimics to spawn?

Mimics can be spawned by the player using the Chest Statue, even prior to Hardmode. However, Mimics spawned this way do not drop any coins or items besides the Mimic Banner.

Where do you find mimics in Minecraft?

Mimics will only spawn and have a 20% chance to naturally replaces chests upon spawning in multiple structures where chests are usually generated. This includes dungeons, abandoned mine shafts, strongholds, desert/jungle temples, Igloos, and Woodland mansions.