  Dark matter might be in the form of a dark plasma in the Milky Way halo.
Specifically, we consider here a hidden sector consisting of a light `dark
electron' and a much heavier `dark proton', each charged under an unbroken
$U(1)'$ gauge symmetry. These self-interacting dark sector particles can also
interact with ordinary matter via the kinetic mixing interaction, and lead to a
signal in dark matter direct detection experiments. Indeed, keV electron
recoils can arise quite naturally in such models from dark electron scattering
off loosely bound atomic electrons. Here we examine the recently reported
XENON1T excess in the context of such a plasma dark matter model. We find that
the observed excess can be explained if kinetic mixing is in the approximate
range: $10^{-12} \lesssim \epsilon \lesssim 10^{-10}$. The allowed parameter
space is consistent with astrophysical and cosmological constraints and
consistent also with other direct detection experiments.
