This township is an almost perfect square, the length from east to west being 1,280 perches and from north to south 1,265 perches. The area is 10,120 acres. Its existence as a township dates from June 3, 1863. This territory had previously been formed into an election precinct as part of Franklin township. The name is that of T. M. Marshall, the attorney by whom the proceedings before the court were conducted.

Big Sewickley creek and Brush creek, a branch of the Conoquenessing, rise in this township. The former flows south, the latter north. Being remote from the larger streams of which they are the affluents, this section of country is distinguished by the absence of hills of the height and prominence which add so much to the beauty of the river valleys, detracting, however, from their agricultural value in corresponding ratio. The northern part of Marshall is probably the largest extent of level country in the county. Farming is the exclusive occupation, and the region is not thickly settled. The population was 705 in 1870, and 748 in 1880. The German element predominates.

It is generally supposed that John Curry was the first settler. John Fowler succeeded to his improvements on Brush creek about 1792. He had three sons, William, Robert M. and John D., all of whom are dead. John H., Esq., Joseph D. and William were sons of Robert. Joseph B. was killed in the battle of the Wilderness; John H. and William are still residing in the township.

Joseph Comjiton located on a tract near the Butler county line in 1805. Samuel Neely settled in the central part of the township near the beginning of this century. His sons were Isaac, William, George and James, of whom the two latter still reside on portions of the old homestead. Robert Peters became a resident about 1815, and settled near the Fowlers, on Brush creek. He had no sons, and the family is not represented here. Pollock became a resident about 1816; none of his family are here. Elijah Boyce came about 1820, and located in the vicinity of the Fowlers. His sons were Stephen, John, George, Robert, Elijah, Thomas and James; all dead but Robert and James, who reside in the west. Robert Forsythe settled prior to 1820 in the vicinity of Boyce. He reared four sons — David, James, Robert and Alexander — all still living. Joseph Stinson came about 1826, and purchased land on Brush creek, near the line of Butler county. He is dead, but his family is still represented here in the female line.

George W. Warren was apprenticed to the elder Fowler in 1826. He continued a resident of the township to the time of his death, in 1879. He was during many years the keeper of the hotel at Brush creek. At the time of his death he was a large landholder. Three sons and three daughters of Mr. W. still reside in this vicinity. David Caldwell came to this township prior to 1830, and passed the balance of his life here. His sons were Alexander, John, William, David, Lewis and Charles; all dead. Some of his grandchildren are now residents here. William Ewart also came before 1830. His sons were William and David, both dead. John Eakin settled near the center of the township before 1820, and died there. His son David is also dead.

The first gristmill in the township was built by David Caldwell, on Brush creek, not far from the Butler county line, between 1820 and 1830. It has gone down. Some years later another was erected on the same stream by John Fowler, Sr. It has also fallen into disuse. A sawmill was also built by Mr. Caldwell near his gristmill. A distillery was conducted by Elijah Boyce, but it has long since gone to decay.

A hotel was established in 1845, by Jonathan Eansom, at Brush creek. It is still kept, but there have been many changes of landlords.

The first search for oil was made in the valley of Brush creek, on the Warren property, by an association of farmers, in 1861. The drill was worked by horse-power, and a leaning tree was utilized for a derrick. After penetrating to the depth of 190 feet the experiment was abandoned. The next attempt was made by the Thornhill Oil company, in 1884, also in the valley of Brush creek. Oil was found at a depth of 1,700 feet, but its mixture with brine rendered it valueless. No further attempts were made till 1887. On the 7th of October in that year oil was found by William Munhall and others at a depth of 1,455 feet. There are now (October, 1888) eight producing wells in the valley of this creek and its branches. It is worthy of remark that the best of these wells is within a few rods of the place where search was first made. Sufficient gas has been found here to run the engines at these wells.

John Coulter established the first store in 1809. The Indian trail from Pittsburgh to the lakes passes diagonally across the township from southeast to northwest. Its route is clearly indicated by arrowheads and other evidences of former Indian travel.

There is one church in the township, a Methodist Episcopal society, organized by Rev. Joshua Monroe. The place of worship is situated contiguous to the Butler county line, and was built in 1853. Blair postoffice was in existence from February 23, 1864, to August 16, 1867. Thornhill was established March 29, 1872.