An 1856 cadastral survey map (tax survey) for T7N R9W shows the Cook homestead along the
waterfront on the north side of Youngs Bay / Youngs River, in Section 18.
The U.S. Bureau of Land Management's General Land Office Records Website (2007) show George W. Cook being granted title to 320.93 acres of parts of T8N R9W Sections 17 and 18, on March 27, 1866 under the 1850 Oregon-Donation Act. This location is on the north side of Youngs Bay and Youngs River, at a point across from Cook Slough.
The 1870 U.S. Coast Survey's map "Columbia River, Sheet No.1" has the slough labeled "Cook's Slough".
The U.S. Board of Geographic Names made the name "Cook Slough" official in 1915. An earlier variant seen was "Cooks Slough".