If you are an Organization-wide Admin, you can add additional departments to your organization.
Click Settings (1) on the left navigation panel, then click Admins (2).
You'll see your departments to the right. To add a new department, click the +Add New Department button (3). The page will refresh automatically.
Once the page reloads, you will see your new department (also named New Department) appear under Departments.
To edit the name, click inside the new department text box, type in the new name, and click Save.
If you've created a new department by mistake, you can also delete it from the Admins page. Just click the red trash icon next to the department you'd like to delete.