Waldo is the surname of:

• Clarence Abiathar Waldo (1852–1926), American mathematician, author, and educator
• Daniel Waldo (1762–1864), veteran of the American Revolutionary War, missionary and U.S. House clergyman
• Daniel Waldo (Oregon pioneer) (1800–1880), American legislator in the Provisional Government of Oregon
• Dr. Dwight B. Waldo (1864–1939), first president of Western Michigan University
• Dwight Waldo (1913–2000), American political scientist
• Edward Hamilton Waldo, birth name of American science fiction author Theodore Sturgeon (1918–1985)
• George E. Waldo (1851–1842), American politician
• Janet Waldo (1920–2016), American actress and voice artist
• Jim Waldo, computer scientist and software architect
• John B. Waldo (1844–1907), jurist and conservationist in Oregon, United States
• Katita Waldo (born 1968), Spanish ballet dancer and ballet master
• Octavia Waldo (born 1929), American writer
• Peter Waldo (1140–1218), founder of a Christian sect called the Waldensians
• Rhinelander Waldo (1877–1927), former U.S. Army captain, Fire and later Police Commissioner of New York City
• Samuel Waldo (1696–1759), Massachusetts land speculator, soldier and political figure
• Samuel Lovett Waldo (1783–1861), American painter
• William Waldo (California politician) (1812–1881)
• William Waldo (Oregon politician) (1832–1911)

Fictional characters

• Mr Waldo is a main character in Dylan Thomas's play Under Milk Wood