VBA_To find a cell value in range_Worksheet change event

[mchilapur]

Dear all,
Somewhere i got messed up with below code. Below is something what i am trying to achieve.

Whenever a user enters new value in any cell of column C:C, vba code must check for only that call value already exists in entire column C:C, if its found, then it must set corresponding column I:I cell value "Multiple". If not found, it must set to "Single".

Challenges faced:
1) Currently i am looping through entire C:C column which is not correct. I want value for cell in column I:I to be updated for new entries in columns C:C only.
(I have values update 5000 + rows..So looping slows down the process)
2) User may enter multiple cell values in one shot (Like, he copies 10 rows of data from some other database and pastes it directly into Excel sheet upto column H:H).

How to i achieve it..? Please help..Attached is the sample work book and has got code it (Which basically doesn't work).

Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Column = 3 Then
    Dim lastRow As Long
    Dim matchFoundIndex As Long
    Dim iCntr As Long
    Dim Rng As Range
    Dim cell As Range
    
    Set Rng = Worksheets("Tracker").Range("C3", Worksheets("Tracker").Cells(Rows.Count, "C").End(xlUp))
    For Each cell In Rng.Cells
        If cell.Offset(0, 6).Value = "" Then
            matchFoundIndex = WorksheetFunction.Match(cell.Value, Rng, 0)
            If cell.Value = matchFoundIndex Then
                cell.Offset(0, 6).Value = "Single"
            Else
                cell.Offset(0, 6).Value = "Multiple"
            End If
        End If
     Next cell
End If
End Sub

[pjwhitfield]

You could set column I to contain the following formula

=IF(ISBLANK(C3),"",IF(COUNTIF(C:C,C3)>1,"Multiple","Single"))

Ive added the ISBLANK to leave the rows that havent yet been completed blank.

[mchilapur]

Not possible using VBA?

[pjwhitfield]

its possible, do you need it to be VBA?

[mchilapur]

Yes please...

[mchilapur]

Dear all,
can anyone please try to get me the logic for this..? I am still not able to do find how best i can do..