Jeff Mark, Altoona’s city administrator for the past 25 years, will retire on Jan. 28. Mark became the eastern Polk County community’s city administrator in October 1996. He currently is the metro area’s longest-serving city administrator or city manager. In the past 25 years, Altoona’s population has grown from 7,800 residents to nearly 20,000. Commercial growth has included the additions of Facebook data centers and construction of the Outlets of Des Moines and Prairie Crossing Shopping Center. A search will be conducted for a new city administrator.