A nonvolatile memory device includes a first semiconductor layer including an upper substrate in which word-lines extending in a first direction and bit-lines extending in a second direction are disposed and a memory cell array, a second semiconductor layer, a control circuit, and a pad region. The memory cell array includes a vertical structure on the upper substrate, and the vertical structure includes memory blocks. The second semiconductor layer includes a lower substrate that includes address decoders and page buffer circuits. The vertical structure includes via areas in which one or more through-hole vias are provided, and the via areas are spaced apart in the second direction. The memory cell array includes mats corresponding to different bit-lines of the bit-lines. At least two of the mats include a different number of the via areas according to a distance from the pad region in the first direction.