Waldo is a city in Columbia County, Arkansas, United States. The population was 1,594 at the 2000 census. Waldo celebrated its 120th year as a city in 2007. The small town was once a booming rail city on the Cotton Belt train route. The city has a rail museum with various displays showing its rail history. The city began to wane in population in the 1950s when neighboring Magnolia began drawing industry. Waldo was also home of the Waldo High School Bulldogs basketball teams.