- Creston is a city in Union County, Iowa, United States. It is located in the southwestern part of the state and has a population of approximately 7,800 people. Creston is known for its historic downtown area, which features many well-preserved buildings from the late 19th and early 20th centuries. The city is also home to Southwestern Community College, which offers a variety of educational programs. Additionally, Creston has several parks and recreational areas, including Green Valley State Park and McKinley Park.