  We report on a full-polarization analysis of the first 25 as yet
non-repeating FRBs detected at 1.4 GHz by the 110-antenna Deep Synoptic Array
(DSA-110) during commissioning observations. We present details of the
data-reduction, calibration, and analysis procedures developed for this novel
instrument. Faraday rotation measures (RMs) are searched between $\pm10^6$ rad
m$^{-2}$ and detected for 20 FRBs with magnitudes ranging from $4-4670$ rad
m$^{-2}$. $15/25$ FRBs are consistent with 100% polarization, 10 of which have
high ($\ge70\%$) linear-polarization fractions and 2 of which have high
($\ge30\%$) circular-polarization fractions. Our results disfavor multipath RM
scattering as a dominant depolarization mechanism. Polarization-state and
possible RM variations are observed in the four FRBs with multiple
sub-components. We combine the DSA-110 sample with polarimetry of previously
published FRBs, and compare the polarization properties of FRB sub-populations
and FRBs with Galactic pulsars. Although FRB polarization fractions are
typically higher than those of Galactic pulsars, and cover a wider range than
those of pulsar single pulses, they resemble those of the youngest
(characteristic ages $<10^{5}$ yr) pulsars. Our results support a scenario
wherein FRB emission is intrinsically highly linearly polarized, and
propagation effects can result in conversion to circular polarization and
depolarization. Young pulsar emission and magnetospheric-propagation geometries
may form a useful analogy for the origin of FRB polarization.
