The population was 3,978 at the 2010 census.
The township is in southwestern Carbon County in the valley of Mahoning Creek, a tributary of the Lehigh River. The township is bordered by the borough of Lehighton to the northeast and by Schuylkill County to the southwest. It is situated near the northeastern end of the Mahoning Hills, the mountainous foothills region to the west of the Lehigh River.
According to the United States Census Bureau, the township has a total area of 23.8 square miles (61.6 km2), of which 23.7 square miles (61.3 km2) is land and 0.1 square miles (0.3 km2), or 0.48%, is water. It is drained by Mahoning Creek, a tributary of the Lehigh River, which forms parts of the township's eastern boundary. The natural northern boundary with Jim Thorpe and Summit Hill is on the south slope of Mauch Chunk Ridge. Its villages include Dry Tavern, Jamestown, Mahoning Valley (also in West Penn Township, Schuylkill County), New Mahoning, Normal Square, and Packerton.
Mahoning's numbered routes include Pennsylvania Route 443, which crosses from U.S. Route 209 on Lehighton's south side west to Route 309 in South Tamaqua, Schuylkill County, and PA 902, which comes southeast over Mauch Chunk Ridge from US 209 in Lansford and Summit Hill to New Mahoning, then turns east to PA 443 in Lehighton with access to US 209 in downtown via Mahoning Street. 209 proceeds north through the township between Lehighton and Jim Thorpe, although this segment is signed southbound.
The township has varied elevations from 450 to 650 feet (140 to 200 m) in the valleys along Route 443 and 902 and rising to 950 to 1,150 feet (290 to 350 m) on the top of Mahoning Mountain in the south and 850 to 1,050 feet (260 to 320 m) on Oriole Hill. The terrain causes the local weather to vary in the winter time from that of the surrounding region. Mahoning Mountain Road is a mile-long hill-climb to a road junction called "Dry Tavern" along a summit of the Mahoning Hills that has many sharp curves and is known throughout the greater Lehighton area as a notorious road in winter time. At the bottom of the mountain it has an elevation of 445 feet (136 m), and at the top it has an elevation of 970 feet (300 m), so it is quite possible for it to be raining at the bottom while having a few inches of snow at the top.
As of the census of 2000, there were 3,978 people, 1,543 households, and 1,131 families residing in the township. The population density was 168.5 people per square mile (65.1/km²). There were 1,693 housing units at an average density of 71.7/sq mi (27.7/km²). The racial makeup of the township was 98.27% White, 0.23% African American, 0.40% Native American, 0.45% Asian, 0.08% from other races, and 0.58% from two or more races. Hispanic or Latino of any race were 0.40% of the population.
There were 1,543 households, out of which 27.7% had children under the age of 18 living with them, 59.8% were married couples living together, 8.2% had a female householder with no husband present, and 26.7% were non-families. 22.2% of all households were made up of individuals, and 12.1% had someone living alone who was 65 years of age or older. The average household size was 2.47 and the average family size was 2.87.
In the township the population was spread out, with 19.8% under the age of 18, 6.4% from 18 to 24, 26.3% from 25 to 44, 26.9% from 45 to 64, and 20.5% who were 65 years of age or older. The median age was 43 years. For every 100 females there were 96.5 males. For every 100 females age 18 and over, there were 94.9 males.
The median income for a household in the township was $35,212, and the median income for a family was $43,897. Males had a median income of $29,016 versus $20,943 for females. The per capita income for the township was $17,330. About 8.6% of families and 10.5% of the population were below the poverty line, including 15.3% of those under age 18 and 3.0% of those age 65 or over.