Lager was born in West Superior, Wisconsin, the only child of Gustav Walfred Lager (a station engineer, who was born in Sweden) and Hilda Marie Erickson Lager (also born in Sweden). Gustav came to the United States in 1890 and Hilda in 1881. They were married on October 28, 1899 in Superior, Wisconsin.
In 2009 she was the subject of a biography, Mildred Lager: History of Her Work with Soyfoods and Natural Foods in Los Angeles (1900-1960).
- Soy Bean Recipes (1942)
- The Useful Soybean: A Plus Factor in Modern Living (1945)
- Soybean Cookbook (1968) [with Dorothea Van Gundy Jones]
- Nguyen, Andrea. (2012). Asian Tofu: Discover the Best, Make Your Own, and Cook It at Home. Ten Speed Press. p. 4. ISBN 978-1607740254
- B. L. (1945). Reviewed Work: The Useful Soybean by Mildred Lager. Far Eastern Survey 14 (16): 232.
- Schneider, B. Aubrey. (1946). Reviewed Work: The Useful Soybean. A Plus Factor in Modern Living by Mildred Lager. The Quarterly Review of Biology 21 (1): 99.
- William Shurtleff; Akiko Aoyagi (2009). Mildred Lager - History of Her Work With Soyfoods and Natural Foods in Los Angeles (1900-1960): Extensively Annotated Bibliography and Sourcebook. Soyinfo Center. ISBN 978-1-928914-26-6.