  The formation of stars in massive clusters is one of the main modes of the
star formation process. However, the study of massive star forming regions is
hampered by their typically large distances to the Sun. One exception to this
is the massive star forming region Cygnus OB2 in the Cygnus X region, at the
distance of about 1400 pc. Cygnus OB2 hosts very rich populations of massive
and low-mass stars, being the best target in our Galaxy to study the formation
of stars, circumstellar disks, and planets in presence of massive stars. In
this paper we combine a wide and deep set of photometric data, from the r band
to 24 micron, in order to select the disk bearing population of stars in Cygnus
OB2 and identify the class I, class II, and stars with transition and
pre-transition disks. We selected 1843 sources with infrared excesses in an
area of 1 degree x 1 degree centered on Cyg OB2 in several evolutionary stages:
8.4% class I, 13.1% flat-spectrum sources, 72.9% class II, 2.3% pre-transition
disks, and 3.3% transition disks. The spatial distribution of these sources
shows a central cluster surrounded by a annular overdensity and some clumps of
recent star formation in the outer region. Several candidate subclusters are
identified, both along the overdensity and in the rest of the association.
