Frank I. Duncan (June 4, 1858 – May 11, 1946) was an American politician, lawyer, judge and newspaper publisher and editor from Maryland.

[1][2] Duncan was appointed as state insurance commissioner by governor Edwin Warfield in 1904.

[1] In 1905, he was appointed associate judge of the Third Judicial Circuit Court, representing Baltimore and Harford counties.

[1] In 1914, Duncan helped the passage of a law that established the juvenile court in Baltimore County.

He also served on the board of visitors of the Maryland State School for the Deaf in Frederick.

He served on the board of directors of the Hospital for Consumptives of Maryland in Towson (also known as the Eudowood Sanatorium).

[1] They had one son and four daughters, John D. C. Jr., Mrs. H. Finley Tucker, Mrs. Ernest C. Hatch, Mrs. William B. Cornell and E.