  We report on the stellar content of the COSMOS two degree field, as derived
from a rigorous star/galaxy separation approach developed for using stellar
sources to define the point spread function variation map used in a study of
weak galaxy lensing. The catalog obtained in one filter from the ACS (Advanced
Camera for Survey on the Hubble Space Telescope) is cross-identified with
ground based multi-wavelength catalogs. The classification is reliable to
magnitude $F_{814W}=24$ and the sample is complete even fainter. We construct a
color-magnitude diagram and color histograms and compare them with predictions
of a standard model of population synthesis. We find features corresponding to
the halo subdwarf main sequence turnoff, the thick disk, and the thin disk.
This data set provides constraints on the thick disk and spheroid density laws
and on the IMF at low mass. We find no evidence of a sharp spheroid edge out to
this distance. We identify a blue population of white dwarfs with counts that
agree with model predictions. We find a hint for a possible slight stellar
overdensity at about 22-34 kpc but the data are not strong enough at present to
claim detection of a stream feature in the halo (abridged).
