A display device includes: a display unit including scan lines, data lines, unit areas corresponding to intersections of the scan lines and the data lines, the unit areas including first unit areas in an effective display area, second unit areas in a dummy area around the effective display area, some of the second unit areas being smaller than the first unit areas, and pixels in the first unit areas; a timing controller configured to receive first data including image data corresponding to the first and second unit areas and to convert the first data into second data corresponding to the effective display area; and a data driver configured to generate a data signal corresponding to the second data. The display unit includes a first horizontal line having fewer pixels than the number of the data lines.