Sedro Woolley, on the north shore of the Skagit River, was founded and first named "BUG" by Mortimer Cook in June of 1884. Bug, refers to the annoying mosquitoes present in the area. It was renamed Sedro when Cook obtained a post office appointment on Dec. 7, 1885.
Sedro is Cook's spelling of "cedro", the spanish word for cedar.
A second town was established in this same area, Woolley. The town was named for Railroad developer Philip A. Woolley
who moved his family from Elgin, Illinois, to Sedro in December 1899.
A couple other towns were also established but they merged on December 19, 1898 as Sedro Woolley. Skagit River Journal