Complex sentence: After the hospital was destroyed by a fire in 1858, architect James Renwick, Jr. designed City Hospital, which prisoners completed construction on in 1861, and served both inmates and New York City's poorer population.
Split into simpler sentences: After the hospital was destroyed by a fire in 1858, architect James Renwick, Jr. designed a new building to be called City Hospital, on which prisoners completed construction in 1861. It served both inmates and New York City's poorer population.