  Dark matter may reside in sector without Standard Model (SM) gauge
interactions. One way in which such a dark sector can still impact SM particles
through non-gravitational interactions is via the "photon portal" in which a
dark photon kinetically mixes with the ordinary SM photon. We study the
implications of this setup for electron recoil events at TEXONO reactor and
nuclear recoil events at the COHERENT experiment. We find that the recent
COHERENT data rules out previously allowed regions of parameter space favored
by the thermal relic hypothesis for the DM abundance. When mapped onto the
DM-electron cross section, we find that COHERENT provides the leading direct
constraints for DM masses < 30 MeV.
