1890 January 0
The Joseph Horne Company was the first large store in the city to substitute electricity for gas illumination. The Pittsburgh Incline to Knoxville was rebuilt.

1890 January 0
Assessed valuation of Pittsburgh real estate totaled $207,300,000. Annual clearings of the Pittsburgh Clearing House Association totaled $786,694,231.

1890 January 0
Population: 238,617; Allegheny City, 105,287; Allegheny County, 551,959.

1890 January 16
A. W. Mellon and his brother, Richard B. Mellon, acquired their first stock in the Pittsburgh Reduction Company.

1890 January 25
Nellie Bly completed her trip around the globe in 72 days 6 hours and 11 minutes.

1890 February 6
Andrew Carnegie repeated his original library proposal first made November 25, 1881, and offered to increase his gift to $1,000,000 to include funds for a museum of natural history and art gallery and for branch libraries.

1890 February 13
The Carnegie Library in Allegheny, the first Carnegie Free Library, was opened to the public after being dedicated by President Benjamin Harrison.

1890 March 0
Oil discovery in Westview.

1890 June 4
Children's Hospital opened.

1890 July 17
The city of Allegheny celebrated its Golden Jubilee.

1890 October 15
Western Pennsylvania Institute for the blind opened in Oakland. The site was given by Mrs. Mary Schenley.

1890 December 13
Marc Connelly, playwright, was born in McKeesport, The Second Avenue Line, the city's first successful electric trolley line, began operating between Downtown and Glenwood.

1891 January 0
The United States Glass Company, one of the country's first large industrial combines, was formed; 17 flintglass factories, most of them in or near Pittsburgh, were acquired.

1891 January 0
A "Roads Congress" was held in Allegheny Carnegie Library lecture hall, under auspices of the Chamber of Commerce, to consider ways of improving public roads.

1891 January 0
Pittsburgh eyes were on nearby Youngwood, where 100 miners were killed in a mine explosion.