New York Harbor that contains a museum and former

Conversion to detention center

Radicals awaiting deportation, 1920
With the passing of the Emergency Quota Act of 1921, the number of immigrants being allowed into the United States declined greatly, ending the era of mass immigration.^{[154][17][155]} Following the Immigration Act of 1924, strict immigration quotas were enacted, and Ellis Island was downgraded from a primary inspection center to an immigrant-detention center, hosting only those that were to be detained or deported (see § Mass detentions and deportations).^{[17][155][156]} Final inspections were now instead conducted on board ships in New York Harbor. The Wall Street Crash of 1929 further decreased immigration, as people were now discouraged from immigrating to the U.S.^[155] Because of the resulting decline in patient counts, the hospital closed in 1930.^{[157][158][159]}
Edward Corsi, who himself was an immigrant, became Ellis Island commissioner in 1931 and commenced an improvement program for the island. The initial improvements were utilitarian, focusing on such aspects as sewage, incineration, and power generation.^[160][161] In 1933, a federal committee led by the Secretary of Labor, Frances Perkins, was established to determine what operations and facilities needed improvement.^[162] The committee's report, released in 1934, suggested the construction of a new class-segregated immigration building, recreation center, ferry house, verandas, and doctors/nurses' quarters, as well as the installation of a new seawall around the island.^{[163][164][165]} These works were undertaken using Public Works Administration funding and Works Progress Administration labor, and were completed by the late 1930s. As part of the project, the surgeon's house and recreation center were demolished,^[125][141] and Edward Laning commissioned some murals for the island's buildings.^[166] Other improvements included the demolition of the greenhouse, the completion of the infilling of the basin between islands 2 and 3, and various landscaping activities such as the installation of walkways and plants.^[167][165] However, because of the steep decline in immigration, the immigration building went underused for several years, and it started to deteriorate.^[163][161]
With the start of World War II in 1939, Ellis Island was again utilized by the military, this time being used as a United States Coast Guard base.^{[168][169][170]} As during World War I, the facilities were used to detain enemy soldiers in addition to immigrants, and the hospital was used for treating injured American soldiers.^[170] So many combatants were detained at Ellis Island that administrative offices were moved to mainland Manhattan in 1943, and Ellis Island was used solely for detainment.^[161][171]
By 1947, shortly after the end of World War II, there were proposals to close Ellis Island due to the massive expenses needed for the upkeep of a relatively small detention center.^[172] The hospital was closed in 1950-1951 by the United States Public Health Service, and by the early 1950s, there were only 30 to 40 detainees left on the island.^{[17][173][174]} The island's closure was announced in mid-1954, when the federal government announced that it would construct a replacement facility on Manhattan.^[175][174] Ellis Island closed on November 12, 1954, with the departure of its last detainee, Norwegian merchant seaman Arne Peterssen.^{[176][177][178]} At the time, it was estimated that the government would save $900,000 a year from closing the island.^[177] The ferryboat Ellis Island, which had operated since 1904, stopped operating two weeks later.^[68][179]