According to the United States Census Bureau, the township has a total area of, of which, of it is land and of it is water. Tohickon Creek flows along the northern edge of the township into Lake Nockamixon at its northeast edge and eastward into the Delaware River and drains most of East Rockhill. The southeast side of the township is drained by the East Branch Perkiomen Creek into the Perkiomen Creek and Schuylkill River. East Rockhill's villages include Hagersville, Rich Hill, Rockhill, Rockhill Station, Rock Ridge, Smoketown, Sterners Mill, Weisel, and White Horse. Natural features include the East Branch Perkiomen Creek, Rock Hill, Three Mile Run, and Tohickon Creek.
As of the 2010 census, the township was 95.8% White, 0.7% Black or African American, 0.2% Native American, 0.6% Asian, and 1.2% were two or more races. 1.6% of the population were of Hispanic or Latino ancestry. As of the census of 2000, there were 5,199 people, 1,828 households, and 1,427 families residing in the township. The population density was 401.5 people per square mile. There were 1,883 housing units at an average density of 145.4/sq mi. The racial makeup of the township was 97.19% White, 0.81% African American, 0.40% Native American, 0.38% Asian, 0.06% Pacific Islander, 0.19% from other races, and 0.96% from two or more races. Hispanic or Latino of any race were 1.25% of the population. There were 1,828 households, out of which 40.4% had children under the age of 18 living with them, 68.6% were married couples living together, 5.8% had a female householder with no husband present, and 21.9% were non-families. 17.1% of all households were made up of individuals, and 5.4% had someone living alone who was 65 years of age or older. The average household size was 2.82 and the average family size was 3.21. In the township the population was spread out, with 28.8% under the age of 18, 6.3% from 18 to 24, 32.5% from 25 to 44, 23.6% from 45 to 64, and 8.9% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 102.1 males. For every 100 females age 18 and over, there were 101.0 males. The median income for a household in the township was $59,663, and the median income for a family was $70,645. Males had a median income of $43,134 versus $30,473 for females. The per capita income for the township was $24,594. About 2.0% of families and 4.9% of the population were below the poverty line, including 3.0% of those under age 18 and 7.6% of those age 65 or over.
Climate
According to the Köppen climate classification system, East Rockhill Twp has a Hot-summer, Humid continental climate. Dfa climates are characterized by at least one month having an average mean temperature ≤, at least four months with an average mean temperature ≥, at least one month with an average mean temperature ≥ and no significant precipitation difference between seasons. Although most summer days are slightly humid in East Rockhill Twp, episodes of heat and high humidity can occur with heat index values >. Since 1981, the highest air temperature was on 07/22/2011, and the highest daily average mean dew point was on 08/12/2016. The average wettest month is July which corresponds with the annual peak in thunderstorm activity. Since 1981, the wettest calendar day was on 08/27/2011. During the winter months, the average annual extreme minimum air temperature is. Since 1981, the coldest air temperature was on 01/22/1984. Episodes of extreme cold and wind can occur with wind chill values <. The average annual snowfall is between and. Ice storms and large snowstorms depositing ≥ of snow occur once every few years, particularly during nor’easters from December through February.
Ecology
According to the A. W. Kuchler U.S. potential natural vegetation types, East Rockhill Twp would have a dominant vegetation type of Appalachian Oak with a dominant vegetation form of Eastern Hardwood Forest. The plant hardiness zone is 6b with an average annual extreme minimum air temperature of. The spring bloom typically begins by April 14th and fall color usually peaks by October 26th.
