Citi Mortgage 1000 Technology Dr, O Fallon, MO63368 Whether a customer is buying a new home or refinancing their current one Citi Mortgage can help. It offers fixed-rate…More and adjustable-rate mortgages and can help buyers and owners figure out the best financial route to take towards home ownership or refinancing. Citi also offers paperless billing and online payment options. This location is a processing loan and paperwork office. It's not an an open-to-the-public branch.