Trewern mission church is located on the north side of the A458 road, between Welshpool and Shrewsbury.
The church was built as a single chambered structure of uncoursed rubble and finer dressings, and a slate roof, with a hipped-roofed porch on the west gable. A narrower chancel of coursed rubble was subsequently added. Windows are of lancet form, paired in the nave.
The church is now derelict and unused.
Sources:
R.Scourfield & R.Haslam, Buildings of Wales: Powys (2013), p.262.
Google Street View, October 2009.

RCAHMW, 19 August 2015.