This township formed part of Chartiers from 1851 to 1860. March 24, 1860, a petition for the division of Chartiers having been presented to the court, John Young, Isaac Walker and Alexander McKee were appointed commissioners to make inquiry as to the propriety of so doing. Their report was favorable, and at a special election, September 9, 1860, there was a large majority in favor of the measure. September 29, 1860, the division as thus proposed was confirmed by the court, and the name "Kirkpatrick" conferred upon the new district. February 9, 1866, the impropriety of so large a name being affixed to so small a township was brought to the notice of the court, with the request that a shorter designation be substituted, and on the same day the name was changed to Union.

Isaac Sellers came from Virginia in 1773, and settled within the present limits of Union township. He was probably the first settler. James Kearns and William Chess, both from Ireland, settled on adjoining tracts in the township, probably in 1774. All the earliest settlers were subjected to frequent alarms by marauding Indians.

The coal-mining interests are important. The Little Saw-Mill Run Railroad company was incorporated July 23, 1850, and the road was opened in April, 1853. It extends from the mouth of Saw-Mill run, at Temperanceville, to Banksville, a distance of three miles. John Haworth is president of the company; Charles S. Fetterman, secretary: Jacob Henrici, treasurer, and Thomas Hartley, general manager. Thousands of tons of coal are mined every year. Shipments are made both by rail and by water, and the sale of the product is controlled by Hartley & Marshall.

The mining industry centers at Banksville, a town of three hundred or four hundred inhabitants, the houses being owned principally by the coal-operators. There is a large and flourishing Methodist Episcopal church. The Baptist Church was organized in 1866, and a church-edifice was built in 1870. The Christian Church was organized in 1882. The town was laid out by George S. Carnahan, on the Alexander Carnahan farm, and was so named from the Banks family, with which Mrs. Carnahan was connected. The postoffice was established in 1878. Isabella Bell is the postmistress.

The population in 1870 was 1,968; in 1880, 2,367.