  We present a measurement of the star formation history of Sextans A, based on
WFPC2 photometry that is 50% complete to V=27.5 (M_V ~+ 1.9) and I=27.0. The
star formation history and chemical enrichment history have been measured
through modeling of the CMD. We find evidence for increased reddening in the
youngest stellar populations and an intrinsic metallicity spread at all ages.
Sextans A has been actively forming stars at a high rate for ~ 2.5 Gyr ago,
with an increased rate beginning ~ 0.1 Gyr ago. We find a non-zero number of
stars older than 2.5 Gyr, due to the limited depth of the photometry, a
detailed star formation history at intermediate and older ages has considerable
uncertainties. The mean metallicity was found to be [M/H] ~- 1.4 over the
measured history of the galaxy, with most of the enrichment happening at ages
of at least 10 Gyr. We also find that an rms metallicity spread of 0.15 dex at
all ages allows the best fits to the observed CMD. We revisit our determination
of the recent star formation history (age <= 0.7 Gyr) using BHeB stars and find
good agreement for all but the last 25 Myr, a discrepancy resulting primarily
from different distances used in the two analyses and the differential
extinction in the youngest populations. This indicates that star formation
histories determined solely from BHeB stars should be confined to CMD regions
where no contamination from reddened MS stars is present.
