Countif with ADO or ScriptingDictionary

Count Col.C in Sheet2, not Sheet1...

Sub test()
    Dim a, b, i As Long, dic As Object
    Set dic = CreateObject("Scripting.Dictionary")
    dic.CompareMode = 1
    With Sheets("sheet2")
        With .Range("c2", .Range("c" & Rows.Count).End(xlUp))
            a = .Value
            b = .Columns(10).Value
        End With
    End With
    For i = 1 To UBound(a, 1)
        If Not dic.exists(a(i, 1)) Then
            dic(a(i, 1)) = Array(b(i, 1), 1)
        Else
            dic(a(i, 1)) = Array(dic(a(i, 1))(0), dic(a(i, 1))(1) + 1)
        End If
    Next
    With Sheets("sheet1")
        With .Range("c2", .Range("c" & Rows.Count).End(xlUp))
            a = .Value
            ReDim b(1 To UBound(a, 1), 1 To 1)
            For i = 1 To UBound(a, 1)
                If dic.exists(a(i, 1)) Then
                    b(i, 1) = dic(a(i, 1))(0)
                    a(i, 1) = dic(a(i, 1))(1)
                Else
                    a(i, 1) = Empty
                End If
            Next
            .Columns(21).Value = b
            .Columns(22).Value = a
        End With
    End With
End Sub