Castle Frank Brook is a buried creek and south-west flowing tributary of the Don River in central and north-western Toronto, Ontario, originating near the intersection of Lawrence Avenue and Dufferin Street.

Residential and industrial development in the former suburban cities of York and North York have obliterated nearly all traces of its original course and topography in the uppermost reaches, but the original stream valley is evident in several older districts bordering the lower reaches.

The channels are all artificially created and run into a storm sewer that carries the remnants of the brook.

The southern section of Vaughan Road roughly parallels the brook's course, bypassing the steep slopes of the Cedarvale ravine.

The site of the original summer home can be seen from aerial photos as a partially cleared area with a ring-like shape.