I assume your Departments form is based on Departments table or on query from this table, and there is a department id field available in this table/query
You create a report with either Departments table or some querystring (with must have Departments table as one of source tables) as it's Source. The query source must contain department id field! The report source (table or query), when opened/run directly, must return the info about all departments.
You create an event script (e.g. OnClick event of some button to open the report. To open the report you use something like (I assume your DepartmentID field is an autonumeric one - in case it is text, you have to enclose the value returned from Me.DepartmentIDControl between ' characters)
Code:
DoCmd.OpenReport "YourReportName", acViewReport, "WHERE DepartmentID = " & Me.DepartmentIDControl
or
DoCmd.OpenReport "YourReportName", acViewReport, "WHERE DepartmentID = '" & Me.DepartmentIDControl & "'"