The numbers tell the story of a city transforming faster than its institutions could keep pace. In 1845, foreign-born residents made up 37 percent of New York City's population. By 1855, that figure had crossed 51 percent. Irish and German arrivals drove the surge, and New York bore the brunt of it. Before the Commissioners of Emigration were established in May 1847, immigration to New York was barely regulated at all. Ships docked, passengers stepped onto the pier, and that was the extent of the process: no passport, no visa, no central processing station. Support for newcomers came largely from private aid societies, like the German Society of the City of New York. But the sheer volume of arrivals, many of them sick, destitute, or both, overwhelmed these private efforts and fueled nativist backlash against the immigrants themselves.

The New York State Legislature created the Board of Commissioners of Emigration to bring order to the chaos. The Board's ten members included appointees of the Governor plus the mayors of New York and Brooklyn. Among their first priorities was caring for sick immigrants, partly out of genuine concern and partly because nativists linked immigration to the spread of disease. Wards Island became the center of that effort. By 1850, the complex had grown to include a refuge building, a hospital, a nursery, and twelve wooden barracks, all connected to the Croton Aqueduct for fresh water. The Refuge and Hospital functioned as a single institution, offering services to immigrants for up to five years after their arrival. By 1870, the hospital had been renamed for Commissioner Gulian C. Verplanck, and the campus had expanded to include fever wards, a dispensary, a dining hall seating 1,200, a surgical ward, and even a lunatic asylum housing 125 patients.

The scale of the operation was staggering. The refuge building alone sheltered 450 destitute women and children. New barracks held another 450 men. Four separate fever ward buildings for men each accommodated 45 patients, while the women's fever ward took 120. A Catholic chapel seated 500 in the nursery building, and a Protestant chapel occupied part of the female medical ward. Yet the facilities were perpetually strained. Irish-American newspapers criticized overcrowding and poor nutrition. The people passing through these wards were not abstractions or statistics; they were families who had survived weeks at sea only to arrive sick, penniless, and at the mercy of an institution that was itself struggling to cope. One remarkable footnote from this era: the hospital's superintendent, Dr. Allan M. Thomas, read about the baby incubator invented in France by Etienne Stephane Tarnier and built a similar device, a claim widely cited as the first use of an incubator in the United States.

In the late 1880s, political opposition mounted against the Board of Commissioners. President Grover Cleveland, who had previously served as Governor of New York, pushed for federal control of immigration. The State Emigrant Landing Depot at Castle Garden closed, and the Wards Island complex followed shortly after. Some immigrant welfare groups protested the closure, but the tide had turned toward federalization, a process that culminated in the opening of Ellis Island in 1892 and the Immigration Act of 1924. The buildings that had once housed the world's largest hospital complex were taken over by the New York City Asylum for the Insane, which became Manhattan State Hospital in 1896 and is now the Manhattan Psychiatric Center. Every structure from the immigration era has been demolished. Today, Wards Island is better known for its public park and wastewater treatment plant than for the hundreds of thousands of immigrant lives that passed through its wards.