An image forming system, image forming apparatus, and method of correcting image density are provided. The system includes a forming unit that forms an image; an acquisition unit that acquires factor information corresponding to a factor which is capable of causing variations in density of the image; a first determination unit that determines a number of marks in accordance with the factor information; a control unit that provides the forming unit with, as the image data, data pertaining to a pattern comprising a plurality of density marks which are different from each other in density and which are equal in number to the number of marks; a detection unit that detects a density of the image formed on the target by the forming unit in relation to the pattern; and a correction unit that corrects the density of the image in accordance with a result of the detection.