function IsCellSelected(StringGrid: TStringGrid; X, Y: Longint): Boolean;
 begin
  Result := False;
  try
  if (X >= StringGrid.Selection.Left) and (X <= StringGrid.Selection.Right) and
  (Y >= StringGrid.Selection.) and (Y <= StringGrid.Selection.Bottom) then
  Result := True;
  except
  end;
 end;
 procedure TForm1.Button1Click(Sender: TObject);
 begin
  if IsCellSelected(stringgrid1, 2, 2) then
  ShowMessage('Cell (2,2) is selected.');
 end;