Private Sub ilDoldur1()
        Dim baglanti As New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source='veritabanının ismi'")
        Dim veriler As New DataTable("iller")
        Dim adapter As New OleDbDataAdapter("select * from iller order by il_ad", baglanti)
        adapter.Fill(veriler)
        ComboBox1.ValueMember = "il_id"
        ComboBox1.DisplayMember = "il_ad"
        ComboBox1.DataSource = veriler
        baglanti.Close()

    End Sub
    Private Sub ilcedoldur1()
        Dim baglanti As New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source='veritabanının ismi'")
        Dim veriler As New DataTable("iller")
        Dim adapter As New OleDbDataAdapter("select * from ilceler where il_id=" & Me.ComboBox1.SelectedValue & " order by ilce_ad", baglanti)
        adapter.Fill(veriler)
        ComboBox2.ValueMember = "ilce_id"
        ComboBox2.DisplayMember = "ilce_ad"
        ComboBox2.DataSource = veriler
        baglanti.Close()
    End Sub

Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
        ilcedoldur1()
           End Sub