"Beginning at the mouth of Brush creek, thence by a straight line to the mouth of Plum creek, on the Allegheny river, thence up the said river to the county line, thence by the said line to the place of beginning." The above is extracted from the minutes of the court of quarter sessions at its first session in 1788, and the township thus described was one of the original subdivisions of the county. In June, 1789, the boundary between Pitt and Plum was established as follows; "Beginning at the mouth of Thompson’s run, thence up the said run to the Lick fork, thence up said fork to the head thereof, thence by a direct line to the mouth of Plum creek." Plum at this time was one of those regularly organized townships on the eastern border of the county. It extended from Versailles to the Allegheny river; below Versailles was Elizabeth, and north of the Allegheny was a section of country as yet unmarked by the influence of civilization.

The following is a partial list of residents in the original territory of Plum in 1808:
Thomas McKee, John Ross, John Little, William Lusk, George Ross, William Loechuer, Abraham Aber, James Richey, Andrew McClintock,
William Hawkles, George Sheimer, James Cochran, David Rankin, William Clugston, William Porter, Philip Shook, Christopher Frederick,
John Porter, Alexander Porter, Alexander Kay, Thomas Dunmore, Thomas McKewry, William White, James P. Mason, Alexander McCullagh,
David Maxel, Henry Cowan, William Myler, David Brown, Daniel Reed, Patrick Porter, James White, Simeon McGraw, Joseph Hall, John Hury,
William Scott, Alexander McMath, Samuel Maginnis, Matthew Simpson, David Herron, Alexander Logan, John Kerr, James Meholm, Jacob Dible,
Robert Cunningham, David Caldwell, Abraham Paxon, Joseph McClintock, William McClelland, Asa Rowley, John Gray, Ebenezer Gill, Abraham Wilson,
William Johnston, William Holloway, Stewart Rowan, Stephen Hull, Daniel Long, James Logan, James Wilkes, David Black, Robert Baxter, James Wilson,
James Osburn, William Folk, Thomas Charlton, Charles Carothers, Robert McElroy, Joseph Ritner, John Hall, William Crumpton, John Byerly, James McCoy,
John Mines, Robert Dinsmore, Thomas McKee,Jr., Samuel Desmond, John Ross, Hugh Marlin, Samuel Caldwell, Thomas Blackburn, James Mains, Robert McCullagh,
Jacob Lane, William McLean, Nathaniel Shaw, Gilbert Grimes, William S. Vigus, Abraham Bollinger, Samuel Coon, Thomas Carit, James Hall, Samuel Barber,
James Sharp, Thomas Wright, Henry Bowman, David Hunnel, Robert Adams, William McJunkin, John Heyl, Robert Baxter, John Black.

Of the above-named persons, William McJunkin is said to have been one of the earliest settlers within the present limits of Plum. The land upon which he lived was surveyed in 1773, under the name of "Greenfield," and is described as being "two miles north of Forbes’ old road."

Plum had a population of 1,446 in 1860; 1,300 in 1870; 1,721 in 1880. Antrim, the first postoffice, was discontinued April 22, 1857, having existed since 1840 (except a short period of suspension), with the following appointments: Samuel Ross, 1840; Robert Ross, 1843; Robert Mehaffey, 1845; Robert M. Ross, 1848; Henry Reister, 1856. There are no villages of importance. New Texas is a hamlet situated about the geographical center of the township, comprising the usual mechanics, local stores, etc. The first postmaster, John A. Conner, was appointed in 1856. Henry R. Toner succeeded him in 1862; John A. Conner, 1866; James Dunn, 1868; Joseph D. Clark, 1869; James B. Duff, 1878; John Lamont, 1881.

Logan’s Ferry, on the Allegheny river and Allegheny Valley railroad, in the northeastern part of the township, derives its name from the Logan family. The earliest representative was Alexander Logan, mentioned in the foregoing list of residents. Gov. Miffiin commissioned him a captain of militia in 1793, and for some years he was justice of the peace. Hugh Logan was appointed postmaster eJune 10, 1844, and Hugh I. Logan April 11, 1871.

In 1870 William Coleman, the Messrs. Carnegie and others purchased large tracts of coal-lands in Plum township, and by consolidating their interests with those of other individual owners formed the New York & Cleveland Gas Coal company, one of the largest mining corporations in Western Pennsylvania. Its lands embrace several thousand acres, extending from the Pennsylvania to the Allegheny Valley railroad, with shipping facilities upon both, the Plum Creek branch of the latter extending a distance of seven miles from Verona inland.

The township sustains nine schools. There are five churches, of which the oldest is Plum Creek Presbyterian. Originally known as Ebenezer, this name was early relinquished in favor of Puckety, under which title it became part of Rev. Francis Laird’s charge in June, 1800, this relation continuing until 1831. Supplies were obtained as early as 1791. During the ministry of Rev. J. D. Moorhead (1865-72), the place of worship was transferred to New Texas, where a church and parsonage were built; but ten years later (April 18, 1876) a reorganization under the name of Laird’s Church was effected, the dedication of the place of worship having occurred June 20, 1876. Unity United Presbyterian Church was organized April 2, 1833, with eleven members. A churchbuilding was begun in 1834, and finished in 1836, and during this period services were conducted in private houses, barns, schoolhouses, and in the open air when the weather permitted. Pastors: William Conner, 1837-49; James Kelso, 1852-72; E. Z. Thomas, 1873-. The church has constituted a separate pastorate since 1864, and was connected with Bethel and Puckety and Tarentum prior to that date. There is a Presbyterian church at Parnassus (Logan’s Ferry), organized in 1842, and a Methodist church (Davidson chapel) in the southwestern part of the township.

In 1956, Plum township was reincorporated as Plum Borough.