The Grey Stone of Trough is an historic boundary marker in Bowland Forest High, in the Trough of Bowland, Lancashire, England.

[1] A Grade II listed structure, erected in 1897 and standing on Trough Road,[2][3] it marks the line of the pre-1974 county boundary between Lancashire and the West Riding of Yorkshire.

[3] Historically, the Trough marked the westernmost boundary of the ancient Lordship of Bowland.

It is in sandstone and has a triangular section with inscriptions on the two sides that face the road.

This article about a Lancashire building or structure is a stub.