  We present results from the Cosmic Evolution Early Release Survey (CEERS) on
the stellar-population parameters for 28 galaxies with redshifts $4<z<9$ using
imaging data from the James Webb Space Telescope (JWST) Mid-Infrared Instrument
(MIRI) combined with data from the Hubble Space Telescope and the Spitzer Space
Telescope. The JWST/MIRI 5.6 and 7.7 $\mu$m data extend the coverage of the
rest-frame spectral-energy distribution (SED) to nearly 1 micron for galaxies
in this redshift range. By modeling the galaxies' SEDs the MIRI data show that
the galaxies have, on average, rest-frame UV (1600 \r{A}) $-$ $I$-band colors
0.4 mag bluer than derived when using photometry that lacks MIRI. Therefore,
the galaxies have lower (stellar)-mass-to-light ratios. The MIRI data reduce
the stellar masses by $\langle \Delta\log M_\ast\rangle=0.25$ dex at $4<z<6$ (a
factor of 1.8) and 0.37 dex at $6<z<9$ (a factor of 2.3). This also reduces the
star-formation rates (SFRs) by $\langle \Delta\log\mathrm{SFR} \rangle=0.14$
dex at $4<z<6$ and 0.27 dex at $6<z<9$. The MIRI data also improve constraints
on the allowable stellar mass formed in early star-formation. We model this
using a star-formation history that includes both a "burst' at $z_f=100$ and a
slowly varying ("delayed-$\tau$") model. The MIRI data reduce the allowable
stellar mass by 0.6 dex at $4<z< 6$ and by $\approx$1 dex at $6<z<9$. Applying
these results globally, this reduces the cosmic stellar-mass density by an
order of magnitude in the early universe ($z\approx9$). Therefore, observations
of rest-frame $\gtrsim$1 $\mu$m are paramount for constraining the stellar-mass
build-up in galaxies at very high-redshifts.
