Добавление колонки в TStringGrid

procedure GridAddColumn(StrGrid: TStringGrid; NewColumn: Integer); 
Var Column: Integer; 
begin 
  StrGrid.ColCount := StrGrid.ColCount+1; 
  For Column := StrGrid.ColCount-1 downto NewColumn do 
    StrGrid.Cols[Column].Assign(StrGrid.Cols[Column-1]); 
  StrGrid.Cols[NewColumn-1].Text := ''; 
end; 

procedure AddColumn(SG : TStringGrid; AtColNumber : integer; 
                    ColWidth : integer = 0); 
var Column : integer; 
    Wdth : integer; 
begin 
  AtColNumber := abs(AtColNumber); 
  SG.ColCount := SG.ColCount + 1; 
  if abs(ColWidth) = 0 then 
     Wdth := SG.DefaultColWidth 
  else 
     Wdth := ColWidth; 
 
  if AtColNumber <= SG.ColCount then begin 
    for Column := SG.ColCount - 1 downto AtColNumber + 1 do begin 
      SG.Cols[Column].Assign(SG.Cols[Column - 1]); 
      SG.Colwidths[Column] := SG.Colwidths[Column - 1]; 
    end; 
 
    SG.Cols[AtColNumber].Text := ''; 
    SG.Colwidths[AtColNumber] := Wdth; 
  end;   
end; 

Взято из https://forum.sources.ru