This township was erected June 26, 1869, by decree of court, upon petition for a division of Sewickley by a line "beginning at the northwest corner of tract numbered eleven in Leet’s district of depreciation lands, and thence along the back line of the river tracts in said district to the northeast corner of tract numbered four, and thence to a point where the public road crosses the Ohio township line." The line thus described was confirmed, and does not pursue a direct course, as is usually indicated upon the map. An effort to have it changed in this respect was made in 1871, but without success.

Jonathan Leet, for whom the township is named, was a surveyor in the employ of the state, and in that capacity he laid out the town of Beaver Falls. A portion of the depreciation lands was assigned to him, and bears the name of "Leet’s district." It adjoins the Ohio river in Beaver county, extending northward many miles. His brother, Maj. Daniel Leet, secured the rich and fertile Sewickley "bottom," comprising a large part of the township. This tract appears in history for the first time in 1779, when the chiefs of the Delaware Indians sought to confer it upon Col. George Morgan in appreciation of his services in their behalf while Indian agent at Fort Pitt during the Revolution. They thus described it; "It begins at the mouth of the run opposite the foot of Montour’s island (in mean the lower end of the island), and extending down the river Ohio to the run next to Logstown — bounded by the said two runs and the river Ohio, and extending back from the river Ohio to the tops of the highest hills — being, we suppose, about three miles in general in a direct line from the river to the tops of the said hills, and about six miles from run to run." But Col. Morgan, foreseeing the consequences of such action on his part, declined the generous offer of his Indian friends, and nearly a score of years later Daniel Leet became the first owner of the tract under the land regulations of the state. A large portion of this estate is still in possession of his descendants. There is reason to believe that the Indians did not leave this section of country until some time after 1800, and in 1796 it is said that there was a village comprising fourteen huts at the mouth of Little Sewickley creek. The English population at that time was of the class known as "squatters," and followed the occupation of "keelboatmen," making long voyages to the lower waters of the Mississippi. Among the permanent settlers was William Leet, a brother of those of that name previously mentioned, who occupied the Leet estate as a tenant. His brother-in-law, John Bean, was also a settler as early as 1796, and his primitive cabin, which stood on the bank of the river near Leetsdale, was long since washed away. His son John survived him. John Way located near the river at a very early day. His house is also gone. His sons were Nicholas, Abisha and James. Mr. Thomas Hoey was also an early settler. William Vickry and sons Philip and others; James Mann and sons Robert, James and William, and John Jackson and his sons John and James are remembered as early residents.

A gristmill was in operation on Little Sewickley creek in 1797. Maj. William Leet did not remove to this region until 1827, three years before his death.

The military road opened by Gen. Wayne in 1798 from Pittsburgh to Legionville was the first in this section of country. It was the principal highway of travel until the opening of the Beaver road, some years later. Both were largely instrumental in developing the agricultural resources of the region; but its present character is suburban rather than agricultural. Few localities in the vicinity of Pittsburgh present equal advantages in this respect. The region is famous for the beauty of its natural scenery, its healthfulness and salubrity, while the Pittsburgh, Fort Wayne & Chicago railroad renders it accessible from all parts of the country. The stations of Fair Oaks, Leetsdale, Shields, Edgeworth, Quaker Valley, Roseburg and Sewickley are all within the limits of Leet township, and at each there is a village, while the Beaver road is virtually lined with handsome residences. Fair Oaks, at the western extremity of the township, is the location of a Baptist church, constituted in 1877. The Leetsdale Presbyterian Church was organized August 1, 1864, at Edgeworth Seminary. A chapel was erected by Mrs. Eliza Shields in 1865, and the cornerstone of the church was laid June 23, 1868. Its dedication occurred November 14, 1869. Mrs. Shields contributed eighteen thousand dollars toward this enterprise. Rev. James M. Platt was pastor of this church from April 15, 1867, to August 9, 1869; Rev. R. S. Van Cleve, from May, 1870, to 1886, and Rev. Johnston, the present pastor, was installed in 1887.

The population of Leet township in 1870 was 629; in 1880, 890. The only postoffice of the township, Leetsdale, was established July 30, 1873.