Sources

Ryall 1696 Cess. Ryal [from MacDonald, 75]
Dalroyal 1747-55 Roy
Ryal 1832 Thomson

“Ryal represents riaghail, a rule; compare an Riaghail, a glen off Glen Lyon, spelled Regill, 1502 (RMS); Regal Burn at the head of Glengavel Water, Avondale, Lanarkshire, in 1478 Regalegill (RMS); le Rigale 1478 (Ant. A. & B.), now Raggal in Boyndie parish, Banff – Thomas Ruddiman, the Latin grammarian, was born appropriately on the farm of Raggal; [148] Carse-regale in Wigtownshire, 1546 (RMS), was apparently near Kilquhokadaill. In Ireland there was Ros Riagla, a ‘promontorium sive collis regulae’ (Onom.), ‘cape or hill of the rule.’ The special meaning of riaghail in names of places is not clear to me.” Watson 1926, p. 147

MacDonald 75 suggested Ryehill. No early forms are offered. As to the issue of the article, Roy’s form Dalroyal suggests a Gaelic origin without an article. Watson (1926, p. 148) also mentions as a parallel: “In Ireland there was Ros Riagla, ‘promontorium sive collis regulae’ (Onom.), ‘cape or hill of the rule.’

A parallel name with the article is given by Robertson in Glen Lyon as An Riaghaill with Tigh na Riaghlach.