The DataGridView controls doesn't have enabled drag and drop reordering rows by default. However, here is the code that you use in the future in your projects in order to implement rows reordering with drag and drop.

In order to make this example to work you need to have a DataGridView control added to your form with a name dataGridView1 and AllowDrop property of the DataGridView set to "true". Also, the necessary events need to be hooked up to the appropriate event handlers.

private Rectangle dragBoxFromMouseDown;
private int rowIndexFromMouseDown;
private int rowIndexOfItemUnderMouseToDrop;
 
private void dataGridView1_MouseMove(object sender, MouseEventArgs e)
{
    if ((e.Button & MouseButtons.Left) == MouseButtons.Left)
    {
        // If the mouse moves outside the rectangle, start the drag.
        if (dragBoxFromMouseDown != Rectangle.Empty &&
        !dragBoxFromMouseDown.Contains(e.X, e.Y))
        {
            // Proceed with the drag and drop, passing in the list item.                    
            DragDropEffects dropEffect = dataGridView1.DoDragDrop(
                  dataGridView1.Rows[rowIndexFromMouseDown],
                  DragDropEffects.Move);
        }
    }
}
 
private void dataGridView1_MouseDown(object sender, MouseEventArgs e)
{
    // Get the index of the item the mouse is below.
    rowIndexFromMouseDown = dataGridView1.HitTest(e.X, e.Y).RowIndex;
 
    if (rowIndexFromMouseDown != -1)
    {
        // Remember the point where the mouse down occurred. 
    // The DragSize indicates the size that the mouse can move 
    // before a drag event should be started.                
        Size dragSize = SystemInformation.DragSize;
 
        // Create a rectangle using the DragSize, with the mouse position being
        // at the center of the rectangle.
        dragBoxFromMouseDown = new Rectangle(
                  new Point(
                    e.X - (dragSize.Width / 2),
                    e.Y - (dragSize.Height / 2)),
              dragSize);
    }
    else
        // Reset the rectangle if the mouse is not over an item in the ListBox.
        dragBoxFromMouseDown = Rectangle.Empty;
}
 
private void dataGridView1_DragOver(object sender, DragEventArgs e)
{
    e.Effect = DragDropEffects.Move;
}
 
private void dataGridView1_DragDrop(object sender, DragEventArgs e)
{
    // The mouse locations are relative to the screen, so they must be 
    // converted to client coordinates.
    Point clientPoint = dataGridView1.PointToClient(new Point(e.X, e.Y));
 
    // Get the row index of the item the mouse is below. 
    rowIndexOfItemUnderMouseToDrop = dataGridView1.HitTest(clientPoint.X, clientPoint.Y).RowIndex;
 
    // If the drag operation was a move then remove and insert the row.
    if (e.Effect== DragDropEffects.Move)
    {
        DataGridViewRow rowToMove = e.Data.GetData(typeof(DataGridViewRow)) as DataGridViewRow;
        dataGridView1.Rows.RemoveAt(rowIndexFromMouseDown);
        dataGridView1.Rows.Insert(rowIndexOfItemUnderMouseToDrop, rowToMove);
 
    }
}