A memory device includes a memory cell array, an address manager and a refresh controller. The memory cell array includes a plurality of memory cells coupled to a plurality of word-lines. The address manager samples access addresses provided from a memory controller to generate sampling addresses and determines a capture address from among the access addresses, based on a time interval between refresh commands from the memory controller. The refresh controller refreshes target memory cells from among the plurality of memory cells based on one of a maximum access address from among the sampling address and the captured address.