Minecraft Diamonds are found below Y-level 16 and become more common the deeper you go. Anything around Y-50 to Y-59 be good.

Diamonds are one of the most valuable resources in Minecraft, but it's not always easy to find them.

In Minecraft, diamonds are valuable for crafting armor, weapons, and tools, found primarily between Y-levels -59 and -64. Methods to locate them include strip mining, exploring lava pools, and ...