Although the land had belonged to the Franciscan monks since the 14th century, the site wasn't developed until 1909. The church and adjacent administration building of St. Joseph's Waldniel were built in just two years. The school building and two other blocks were completed in 1913. The Franciscan monks, who cared for 600 male patients, most of them mentally handicapped, remained active there until 1937. On the eve of World War II, the previously self-supporting monastery was driven to bankruptcy by the Nazis. The last monks left on May 23, 1937.

The site was then taken over by the then Prussian Rhine Province, only to shortly afterwards enter the darkest part of its history, when the Nazis established the "Waldniel Institute" here and more than 500 people, including 30 children, were killed there under the "National Socialist euthanasia program."