Calchfynydd (Welsh calch "lime" + mynydd "mountain") was an obscure Britonnic kingdom or sub-kingdom of sub-Roman Britain.
The name survives in the epithet of Cadrawd Calchfynydd, apparently a 6th-century ruler of the district.
Welsh sources refer to Cadrawd as one of the Gwyr y Gogledd or 'Men of the North', suggesting the area was located somewhere in northern Britain.
William Forbes Skene suggested an identification with Kelso (formerly Calchow) in southern Scotland and Rachel Bromwich agrees that a location somewhere in the Hen Ogledd is most likely.
[1] Alistair Moffat in his history of Kelso supports this position, citing early references to "Chalchou," as well as the chalk area and Chalkheugh Terrace.