Frederick W. Mulkey (January 6, 1874 - May 5, 1924) was a United States Senator from Oregon. Born in Portland, he attended the public schools, graduated from the University of Oregon at Eugene in 1896 and from the New York Law School of New York City in 1899. He was admitted to the Oregon bar and commenced the practice of law at Portland. He was a member of the Portland City Council from 1900 to 1902, and served as president in 1901. He was chairman of the Oregon State Tax Commission in 1905-1906.
Mulkey was elected on November 6, 1906 as a Republican to the U.S. Senate to fill the vacancy caused by the death of John H. Mitchell and served from January 23, 1907, until March 3, 1907; he was not a candidate for reelection in 1907. He resumed the practice of law in Portland and was chairman of the city's Public Docks Commission from 1911 to 1916. On November 5, 1918, he was again elected to the U.S. Senate, this time to fill the vacancy caused by the death of Harry Lane and served from November 6, 1918, until his resignation, effective December 17, 1918. He resumed the practice of his profession in Portland and was chairman of the Multnomah County Tax Supervising and Conservation Commission from 1921 to 1924. He died in Portland in 1924; interment was in Riverview Cemetery.
Joseph Norton Dolph, also a U.S. Senator from Oregon, was Frederick Mulkey's uncle.