An integrated circuit device includes a first conductive pattern on a substrate, a second conductive pattern surrounding at least a portion of the first conductive pattern and covering a lower portion of a sidewall of the first conductive pattern, an upper insulating structure on the first conductive pattern and the second conductive pattern, and an upper conductive pattern extending in a vertical direction through the upper insulating structure. The upper conductive pattern includes a main plug portion overlapping the first conductive pattern and the second conductive pattern in the vertical direction, and a vertical extension portion extending from a local region of the main plug portion toward the substrate, the vertical extension portion covering an upper portion of the sidewall of the first conductive pattern and overlapping the second conductive pattern in the vertical direction.