Rather than set the whole DGV to be readonly, you'll need to set each individual column to be readonly except the one which you want to be editable.

Suppose, for example, that you have a DGV called dataGridView1 and you want all columns to be readonly except the one with a header containing "Address".

The code to do that would be:

foreach (DataGridViewColumn column in dataGridView1.Columns)
{
    if (column.HeaderText != "Address") column.ReadOnly = true;
}