Minecraft wiki entry for Pillager, associated text: Pillagers continually spawn in a 72×54×72 block volume centered on the top floor. They may spawn on any valid opaque block as long as the sky light level is 11 or lower, and the block light level is 8 or lower, but can also spawn on grass blocks or sand regardless of sky light level. There can be unlimited pillagers that spawn in outposts naturally, limited only by the natural spawning rules.