Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

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.Top) 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;