Try this...
for (int i = 0; i < RDL.Count; i++)
{
TableRow tr = new TableRow();
TableCell td = new TableCell();
TextBox textBox = new TextBox();
td = new TableCell();
td.Width = Unit.Pixel(145);
textBox = new TextBox();
textBox.Text ="From DB";
td.Controls.Add(textBox );
if(i=RDL.Count-1)
{
tr.Controls.Add(td);
}
}