Cogan House Township was formed parts of Jackson and Mifflin townships on December 6, 1843. The source of Larrys Creek is in Cogan House Township, just south of the hamlet of Steam Valley. It flows west-southwest through the village of Cogan House, and then under the Cogan House Covered Bridge. The bridge is also known as the "Buckhorn Covered Bridge" or the "Larrys Creek Covered Bridge". A petition from the citizens of Cogan House Township for a bridge to be built was filed on September 4, 1876. The 90 foot long Burr arch truss bridge was built in 1877, rehabilitated in 1998, and is on the National Register of Historic Places. Larrys Creek was vitally important to the economic development of Cogan House Township. During the height of the lumber era that swept through Pennsylvania in the mid-to-late 19th century, Larrys Creek was used to float logs from the hills of the township to the lumber industry in nearby Williamsport on the West Branch Susquehanna River. The township is named for David Cogan, a pioneer who settled on Larrys Creek in 1825. Cogan was one of the few settlers in the area for many years, but wearying of his isolation, he left his homestead in 1842, as did a neighbor named Carter. Cogan's and Carter's houses were used by hunters and travellers. The name Cogan's House was given to the area, hence the name, Cogan House.
As of the census of 2000, there were 974 people, 359 households, and 273 families residing in the township. The population density was 13.9 people per square mile. There were 451 housing units at an average density of 6.5/sq mi. The racial makeup of the township was 99.38% White, 0.10% African American, 0.10% Native American, 0.10% from other races, and 0.31% from two or more races. Hispanic or Latino of any race were 0.51% of the population. There were 359 households, out of which 29.8% had children under the age of 18 living with them, 68.0% were married couplesliving together, 4.7% had a female householder with no husband present, and 23.7% were non-families. 18.1% of all households were made up of individuals, and 7.5% had someone living alone who was 65 years of age or older. The average household size was 2.66 and the average family size was 3.08. In the township the population was spread out, with 24.9% under the age of 18, 7.6% from 18 to 24, 26.9% from 25 to 44, 27.9% from 45 to 64, and 12.6% who were 65 years of age or older. The median age was 39 years. For every 100 females there were 102.5 males. For every 100 females age 18 and over, there were 103.6 males. The median income for a household in the township was $36,172, and the median income for a family was $40,192. Males had a median income of $31,875 versus $20,350 for females. The per capita income for the township was $15,345. About 8.0% of families and 9.5% of the population were below the poverty line, including 10.3% of those under age 18 and 9.7% of those age 65 or over.
