Sixty-one-year-old John Manning entered the plea Tuesday in federal court.
Manning was suspended without pay from his position in Wilmington's personnel department after his arrest in October. He resigned in April.
Federal agents found more than 600 pornographic images of children on computers seized at Manning's home. The investigation began after agents learned Manning had paid for access to a child porn Web site.
His attorney, Christopher Koyste, says Manning is ashamed of his actions.
Manning is to be sentenced in August.
Information from: The (Wilmington, Del.) News Journal, http://www.delawareonline.com
