  We map the full extent of a rich massive young cluster in the Cep OB3b
association with the IRAC and MIPS instruments aboard the {\it Spitzer} Space
Telescope and the ACIS instrument aboard the $\it{Chandra}$ X-Ray Observatory.
At 700 pc, it is revealed to be the second nearest large ($>1000$ member),
young ($< 5$ Myr) cluster known. In contrast to the nearest large cluster, the
Orion Nebula Cluster, Cep OB3b is only lightly obscured and is mostly located
in a large cavity carved out of the surrounding molecular cloud. Our infrared
and X-ray datasets, as well as visible photometry from the literature, are used
to take a census of the young stars in Cep OB3b. We find that the young stars
within the cluster are concentrated in two sub-clusters; an eastern
sub-cluster, near the Cep B molecular clump, and a western sub-cluster, near
the Cep F molecular clump. Using our census of young stars, we examine the
fraction of young stars with infrared excesses indicative of circumstellar
disks. We create a map of the disk fraction throughout the cluster and find
that it is spatially variable. Due to these spatial variations, the two
sub-clusters exhibit substantially different average disk fractions from each
other: $32% \pm 4%$ and $50% \pm 6%$. We discuss whether the discrepant disk
fractions are due to the photodestruction of disks by the high mass members of
the cluster or whether they result from differences in the ages of the
sub-clusters. We conclude that the discrepant disk fractions are most likely
due to differences in the ages.

Solar and Stellar Astrophysics;Astrophysics of Galaxies