Ion Lewis (1853 – August 29, 1933) was a founding member of Whidden & Lewis, a prominent architectural firm in Portland, Oregon, United States around the beginning of the 20th century. The firm was formed with partner William M. Whidden. Their residential buildings were mostly in the Colonial Revival style, while their commercial buildings were primarily in the twentieth-century classical style. The commercial buildings often featured brick, along with terra cotta ornamentation. Many of their buildings are listed on the National Register of Historic Places (NRHP). Lewis was born in 1853 in Boston, Massachusetts, and moved to Portland in 1881. Some buildings he designed include Portland City Hall, the Multnomah County Courthouse, and the Forestry Building from the Lewis & Clark Exposition. Lewis died on August 29, 1933.