A nonvolatile memory device includes multi-level cells in a memory cell array including a plurality of memory blocks, and each of the memory blocks includes a plurality of pages. A method of operating the nonvolatile memory device includes pre-programming multi-bit data in a pre-program block of the memory blocks, dividing the multi-level cells into a plurality of state groups based on state codes indicating states of the multi-level cells to generate digest data indicating state group codes corresponding to the state groups, and programming the digest data in a digest block of the memory blocks.