Count Used Cells Of Range

I'm trying to create a quick macro that tells me the number of active rows in a spreadsheet with just one column, and then copies the value of that variable and places it into an excel spreadsheet. For Counting the rows in Column A, I have:

Sub countRows()
Dim RowCount As Integer
RowCount = Range("A1", Range("A1").End(xlDown)).Rows.Count
End Sub

How could I get the value of RowCount to be entered into the excel spreadsheet, say, in cell D5?