Complex sentence: On September 4,1839, Mount Morris Square became a 20 acre residential square which was formerly a race track for horses, out of 173 acres owned by the Benson family land grant farm.
Split into simpler sentences: On September 4,1839, Mount Morris Square became a 20 acre residential square which was formerly a race track for horses. This was 20 out of 173 acres owned by the Benson family land grant farm.