  We study dark matter production from mediator decays in scenarios with an
epoch of early matter domination. Particles that mediate interactions between
dark matter and the standard model particles are kinematically accessible to
the thermal bath as long as their mass is below the reheating temperature of
the Universe after inflation. Decay of on-shell mediators can then lead to
copious production of dark matter during early matter domination or a preceding
radiation-dominated phase. In particular, for mediators that are charged under
the standard model, it can exceed the standard freeze-in channel due to inverse
annihilations at much lower temperatures (often by many orders of magnitude).
The requirement to obtain the correct relic abundance severely constrains the
parameter space for dark matter masses above a few TeV.
