unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  Grids, StdCtrls;

type
  TForm1 = class(TForm)
    StringGrid1: TStringGrid;
    procedure StringGrid1DrawCell(Sender: TObject; ACol, ARow: Integer;
      Rect: TRect; State: TGridDrawState);
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

const
 cell_x = 2;
 cell_y = 2;

var
  Form1: TForm1;
  CheckBox1: TCheckBox;

implementation

{$R *.DFM}

procedure TForm1.StringGrid1DrawCell(Sender: TObject; ACol, ARow: Integer;
  Rect: TRect; State: TGridDrawState);
var
 r:trect;
begin
 if(cell_x>=StringGrid1.LeftCol) and
   (cell_x<=StringGrid1.LeftCol+StringGrid1.VisibleColCount) and
   (cell_y>=StringGrid1.TopRow) and
   (cell_x<=StringGrid1.TopRow+StringGrid1.VisibleRowCount) then
     CheckBox1.Visible:=true
 else
     CheckBox1.Visible:=false;

 if (acol=cell_x) and (arow=cell_y) then
 begin
   r:=stringgrid1.CellRect(cell_x,cell_y);
   r.Left:=r.left+stringgrid1.left+2;
   r.right:=r.right+stringgrid1.left+2;
   r.top:=r.top+stringgrid1.top+2;
   r.bottom:=r.bottom+stringgrid1.top+2;
   CheckBox1.BoundsRect:=r;
 end;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
 CheckBox1:=TCheckBox.Create(form1);
 CheckBox1.parent:=form1;
 CheckBox1.Caption:='proba';
end;

end.