inceleyemiyorum ama bende şu şekilde 

Private Sub ilDoldur()
        Dim baglanti As New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source='access.mdb'")
        Dim veriler As New DataTable("il")
        Dim adapter As New OleDbDataAdapter("select * from tblil order by il", baglanti)
        adapter.Fill(veriler)
        cbIl.ValueMember = "id"
        cbIl.DisplayMember = "il"
        cbIl.DataSource = veriler
    End Sub
    

  Private Sub ilceDoldur()
        Dim baglanti As New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source='access.mdb'")
        Dim veriler As New DataTable("ilce")
        Dim adapter As New OleDbDataAdapter(String.Format("select * from tblilce where il_ID={0}", cbIl.SelectedValue.ToString), baglanti)
        adapter.Fill(veriler)
        cbIlce.DataSource = veriler
        cbIlce.DisplayMember = "ilce"
    End Sub