What was the first skyscraper?
The Home Insurance Building in Chicago gets the title in most books. It is a reasonable answer and a contested one, because six buildings have a claim and each one wins under a different definition.
The short answer
The Home Insurance Building at LaSalle and Adams in Chicago, finished in 1885 to a design by William LeBaron Jenney. It opened with 10 floors at 138 ft (42 m), gained two more in 1891 and reached 55 m. No earlier building hung its outer walls on a metal skeleton over that many floors, and that is the feature the title usually rewards.
A building of 12 floors would not register as tall today. In 1885 it was the tallest commercial block in Chicago, and the engineering inside it is why the Burj Khalifa is possible.
The Home Insurance Building
The Home Insurance Company of New York wanted a fireproof office block with daylight in every room on a narrow lot. Jenney, trained as an engineer, answered with a grid of iron and steel columns and beams that took the floor loads and the weight of the exterior. Construction began on 1 May 1884. Tenants got large windows because the masonry between them no longer had to hold anything up.
Why it counts, and why some dispute it
The case for it is the skeleton frame. Before 1884, a tall masonry building carried its own weight in its walls, and the walls at street level grew thicker as the floors went up. Jenney's frame moved that job to metal, so height stopped being limited by how much stone a ground floor could stand on. Rolled Bessemer steel beams went into the upper floors, among the first structural steel used in a building anywhere.
The case against it has two parts. The columns were largely cast iron, a material already used in storefronts for decades, and parts of the building still leaned on masonry: the party walls at the sides did structural work, and the frame had no bracing designed for wind. When the building came down in 1931, a committee of Chicago engineers examined the exposed structure and reported in 1932 that the walls were not true curtain walls. They declined to name any single building as the first skyscraper and said the Tacoma Building had gone further.
The title also had publicists. Jenney and his Chicago colleagues promoted the building's priority for years against claims from New York and from Leroy Buffington in Minneapolis, and the definition that settled on skeleton framing in iron happens to be the one Chicago wins. The companion page covers Jenney himself and that fight over credit.
The other buildings with a claim
Equitable Life Building, New York, 1870. Seven floors of load-bearing masonry, and the first office building in the world with passenger elevators from the start. If a skyscraper is a building people reach by machine rather than stairs, this is the first one. Its walls carry their own weight, so it fails the frame test. It burned in 1912.
Tacoma Building, Chicago, 1889. Holabird & Roche, 13 floors. George A. Fuller riveted its iron and steel members together instead of bolting them, and its two street facades are genuine curtain walls, carried entirely by the frame. The 1932 engineers preferred it to the Home Insurance Building on exactly that point. It was demolished in 1929.
Rand McNally Building, Chicago, 1890. Burnham & Root, 10 floors, 45 m. The first building framed in steel alone, with no cast iron in the skeleton. Every tall building since uses this method rather than Jenney's mixture. It lasted 21 years and came down in 1911.
Wainwright Building, St Louis, 1891. Louis Sullivan and Dankmar Adler, 10 floors, 41 m. The first tall building that looks like one. Sullivan ran unbroken brick piers from the base to the cornice so the eye reads the height instead of a stack of separate stories, and the earlier Chicago blocks look like warehouses beside it. Sullivan's work has its own page. The Wainwright still stands and holds state offices.
Ingalls Building, Cincinnati, 1903. Elzner & Anderson, 16 floors, 64 m, the first skyscraper of reinforced concrete. Engineers expected it to crack apart under its own weight; a reporter waited across the street the night the forms came off. It is still there, now a hotel.
The first skyscraper with more than 100 floors
The Empire State Building, finished in 1931 with 102 floors at 381 m. It passed 100 floors 46 years after the Home Insurance Building opened, and in the same year that building was torn down. The height record has moved on since.
Can you visit it?
No. The Home Insurance Building was demolished in 1931, one of six buildings cleared for the Field Building, now 135 South LaSalle Street. A plaque inside the lobby calls the vanished building the father of the skyscraper. The demolition is how the 1932 report got to inspect the frame in the first place.
So which answer is right?
Pick the criterion first and the building follows. By elevator, the Equitable Life Building of 1870. By metal skeleton carrying the walls, the Home Insurance Building of 1885. By true curtain wall, the Tacoma Building of 1889. By all-steel frame, the Rand McNally Building of 1890. By appearance, the Wainwright Building of 1891. By material, the Ingalls Building of 1903 opened the concrete line. Skyscraper Day on 3 September marks the whole sequence, not one building in it.