A non-volatile memory device, a method of operating the non-volatile memory device, and a memory system including the non-volatile memory device are provided. A non-volatile memory device includes a memory cell array including a plurality of memory cells configured to be each programmed to one state of a plurality of states, a page buffer circuit including a plurality of page buffers configured to each store received data as state data indicating a target state of a corresponding one of the plurality of memory cells, the page buffer circuit being configured to perform a state data reordering operation of changing a first state data order into a second state data order during performance of a program operation on selected memory cells of the plurality of memory cells, and a reordering control circuit configured to control the page buffer circuit to perform the state data reordering operation simultaneously with the program operation.