Waldo Porter Johnson (September 16, 1817August 14, 1885) was a United States Senator from Missouri, and later a member of the Confederate Congress during the American Civil War. Born in Bridgeport, Virginia, he attended public and private schools, graduated from Rector College (Pruntytown, Virginia) in 1839. He studied law and was admitted to the bar, commencing practice in Harrison County, Virginia in 1841. He moved to Osceola, Missouri in 1842 and continued the practice of law, and served in the Mexican-American War as a member of the First Missouri Regiment of Mounted Volunteers. In 1847 he was a member of the Missouri House of Representatives and was elected circuit attorney in 1848 and judge of the seventh judicial circuit in 1851. He resigned in 1852 and resumed the practice of law.