New York is near the northern limit of the Glossy Ibis' breeding range, with breeding populations being restricted to non-barrier and salt marsh islands in Long Island and around New York City, along with breeding on one of the Four Brothers Islands on southern Lake Champlain (McGowen and Corwin 2008; New York Natural Heritage Program 2009).

Glossy Ibis were first recorded as breeding in New York at Jamaica Bay National Wildlife Refuge in 1961, with three nesting pairs observed (Post 1962). In 1979, a maximum of 892 pairs were recorded in the New York City area and populations since then have been steadily declining. During the Breeding Bird Atlas surveys, the number of confirmed breeding blocks declined from 19 during the 1980-1985 surveys to 14 during the 2000-2005 surveys (McGowan and Corwin 2008). Surveys conducted under the New York City Audubon Harbor Herons Project show a 27% decline in the number of nests observed between 2004 (350 nests) to 2007 (254 nests), with nesting occurring on only three islands in the New York City area (Bernick 2007). During the 2007 Long Island Colonial Waterbird surveys conducted by the New York State Department of Environmental Conservation, Glossy Ibis were reported as active on 8 of the 29 known colonies around Long Island (New York State Department of Conservation 2007; New York Natural Heritage Program 2009).

The Range of the Glossy Ibis continues to expand worldwide. Populations in the United States have also been expanding from a local breeding population in Florida in the early 1900s to breeding populations occurring in every state along the Atlantic Coast except for New Hampshire, as well as breeding along Louisiana's Gulf Coast over the course of the 20th century. However, numbers of breeding Glossy Ibis have been on a decline since the 1970s. Due to their dark plumage, it is difficult to accurately survey for Glossy Ibis and numbers may fluctuate from year to year (Davis and Kritcher 2000).