  Spitzer IRAC observations and stellar photometric catalogs are presented for
the Massive Young Star-Forming Complex Study in the Infrared and X-ray
(MYStIX). MYStIX is a multiwavelength census of young stellar members of twenty
nearby (d < 4 kpc), Galactic, star-forming regions that contain at least one O
star. All regions have data available from the Spitzer Space Telescope,
consisting of GLIMPSE or other published catalogs for eleven regions and
results of our own photometric analysis of archival data for the remaining nine
regions. This paper seeks to construct deep and reliable catalogs of sources
from the Spitzer images. Mid-infrared study of these regions faces challenges
of crowding and high nebulosity. Our new catalogs typically contain fainter
sources than existing Spitzer studies, which improves the match rate to Chandra
X-ray sources that are likely to be young stars, but increases the possibility
of spurious point-source detections, especially peaks in the nebulosity. IRAC
color-color diagrams help distinguish spurious detections of nebular PAH
emission from the infrared excess associated with dusty disks around young
stars. The distributions of sources on the mid-infrared color-magnitude and
color-color diagrams reflect differences between MYStIX regions, including
astrophysical effects such as stellar ages and disk evolution.
