Dalrymple Forum an oldie but goodie!
Local. Taken from the lands and barony of Dalrymple, in Ayrshire, Scotland. The name is said to be a corruption of the Gaelic Dale—roi—milleadh, which signifies "the valley of the slaughter of kings," and the place was so called from a battle fought there before the Christian era, in which two kings, Fergus and Coilus, were slain. According to others, it signifies "the valley of the crooked pool." I think the name signifies "the valley on the margin of the pool," from the Welsh Dol, a valley; the edge or border, and a pool. It is very nearly the same in Gaelic; Bail, a vale, troimh , (Gaelic) by, along with the whole extent, and poll, a small lake.
— An Etymological Dictionary of Family and Christian Names (1857) by William Arthur
(Celtic) belonging to Dalrymple (Ayr), 15th cent. Dalrumpyll-the Field of the Crooked Pool [Gaelic dail-chruim-puill] The village of Dalrymple is pleasantly situated on the Doon, where that river has a considerable bend.—Nat Gaz.
— Surnames of the United Kingdom (1912) by Henry Harrison