Set value to unbound column

To set value in unbound column cells you have to handle CellFormating event. Then, check DataGridViewCellFormattingEventArgs and set value. For example:

private void dataGridView1_CellFormatting(object sender, DataGridViewCellFormattingEventArgs e)
{
if (e.ColumnIndex == 2)
{
e.Value = "Test";
}
}