The "Battle of Crogen" does not seem to have been a battle, more one of a series of minor harassments of Henry II's army by the Welsh. The locations of the skirmishes could be in England, or could be at Tregeiriog – see J.E.Lloyd, A History of Wales, vol II, 1912, p.516 and footnote 117.
"1165: In this year King Henry came to Oswestry, thinking to annihilate all Welshmen. And against him came Owain and Cadwaladr, sons of Gruffudd ap Cynan, and all the host of Gwynedd with them, and Rhys ap Gruffudd and with him the host of Deheubarth, and Owain Cyfeiliog and the sons of Madog ap Maredudd and the host of all Powys with them, and the two sons of Madog ab Idnerth and their host. And both sides stayed in their tents until the king moved his host into Dyffryn Ceiriog and there he was defeated at Crogen."
Source: The Chronicle of Ystrad Fflur.
Henry II led his army to the river Ceiriog, where a party of Welsh suddenly attacked the van of Henry's army and in the action that ensued, since called the battle of Crogen, many were killed on both sides.
Source: Entry for Denbighshire in Lewis S, 'A Topographical Dictionary of Wales' (1849).
A commemorative plaque (nprn 412333) has been affixed to Castle Mill Bridge (nprn 310228) and refers to the "Battle of Crogen" having been fought "nearby in August 1165 . . . between Henry II, King of England (r.1154-89) and Welsh forces under Owain Gwynedd (1137-70)" The plaque was unveiled on 04 March 2009 by Wrexham Borough Council Leader Aled Roberts.
B.A.Malaws, RCAHMW, 29 September 2010.