Blackwell's Island was later named Welfare Island, and subsequently renamed Roosevelt Island. Due to the number of hospitals and asylums, the area was designated as a Hospital Park. By the mid-twentieth century, it became a mixed-use zone, through the introduction of residential developments, and by the twentieth-first century, a satellite campus of Cornell University and Franklin Roosevelt's Four Freedom Park was established at the Southern end of the Island.

The full name of Luke Evans' character is John Schuyler Moore. Schuyler is an old New York Dutch family whose roots can be traced back to well before the founding of the nation and has close ties to the Roosevelt clan. A well-known ancestor of Moore was Elizabeth Schuyler, wife of Alexander Hamilton.

The show is based on the novel "The Alienist" by Caleb Carr.

St. Elizabeths Hospital was the site of a Federal Mental Asylum frequented by members of the armed services who were deemed unfit for duty. In the early twenty-first century, it is slated for redevelopment as the Headquarters of the Department of Homeland Security.

An alienist is a term for a psychiatrist who assesses the competence of a defendant in a law court.

In the original novel, the character John Moore is a crime reporter. In the TV series, he is an illustrator. In one episode, Moore purchases a typewriter at a tricky tray event and tells Sarah Howard that he is interested in becoming a writer.

To put the show setting into context, the consolidation of New York--that is, inclusion of the four outer boroughs of Brooklyn, Queens, Bronx, and Staten Island into Manhattan--did not take place until 1898, two years after the established series date of 1896.

The former location of the "Old Met," Old Metropolitan Opera building, was at the corner of 39th Street and Broadway. The old building was known as the "Diamond Horseshoe," and one of the major reasons why the Opera company removed themselves to Lincoln Center was that the stage and backstage area had very little room to accommodate the players and props.

High Bridge Tower is next to High Bridge. At one time, it served as an aqueduct which brought water from upstate into New York City.

People with mental illness were once considered "alienated from society," hence those who treated them being referred to as alienists.

The show takes place in 1896 New York City.

The allusion to Immigration Station turned Aquarium, is now known as Castle Clinton or Castle Garden.

The main titles for the series were created by the design studio "Elastic," the same studio responsible for the intro of True Detective (2014) and Game of Thrones (2011).

The Croton Reservoir was located where Main New York Public Library and Bryant Park now reside.

The serial killer in the series is based upon known serial killer Albert Fish, also known as "The Grey Man," hence the silver smile reference. He abducted, murdered, and ate Grace Budd and then sent a letter to her parents detailing how he ate her and how he did not violate her. The same happens in this series.

John briefly interacted with a member of the Astor family. The family made their money in the fur trade in the Western United States and what remains of their legacy are: Waldorf-Astoria Hotel and a district in Queens known as Astoria.