PL/SQL :: Count Number Of Employees In Every Department - Group By Clause Not Working

I have two columns Department and EmpName:

Department EmpName
____________________________________
Sales empname1
Sales empname2
Marketing empname3
Development empname4

Now I want to count the number of employees in every department. I want the output to be

Department Total
______________________
Sales 2
Marketing 1
Development 1

I am retrieving names of the department through a subquery

The query I am trying to execute is:

SELECT Department, Employee FROM
( SELECT ...query from other table) AS Department, count( A.EmpName) AS Employee
FROM Employer A, EmployeeInfo B
WHERE (A.EmpID = B.EmpID AND A.EmpCategory like 'Category2')
GROUP BY Department

I know that you cannot group by using aliases and hence a little work around, but still the query isn't working.