Sisseln has an area, as of 2009[update], of 2.52 square kilometers (0.97 sq mi). Of this area, 0.82 km2 (0.32 sq mi) or 32.5% is used for agricultural purposes, while 0.5 km2 (0.19 sq mi) or 19.8% is forested. Of the rest of the land, 0.89 km2 (0.34 sq mi) or 35.3% is settled (buildings or roads), 0.38 km2 (0.15 sq mi) or 15.1% is either rivers or lakes.
Of the built up area, industrial buildings made up 9.5% of the total area while housing and buildings made up 6.0% and transportation infrastructure made up 12.7%. Power and water infrastructure as well as other special developed areas made up 5.6% of the area while parks, green belts and sports fields made up 1.6%. Out of the forested land, 13.9% of the total land area is heavily forested and 6.0% is covered with orchards or small clusters of trees. Of the agricultural land, 27.4% is used for growing crops and 4.8% is pastures. All the water in the municipality is in rivers and streams.
The blazon of the municipal coat of arms is Vert a Bend sinister wavy Argent and from it issuant towards base a Bendlet wavy and in chief a Trident of the same in bend downwards. The two wavy bars represent the Rhine River (the larger one) and the Sissle River (the smaller one).“
Sisseln has a population (as of December 2020[update]) of 1,661As of June 2009[update], 17.0% of the population are foreign nationals. Over the last 10 years (1997–2007) the population has changed at a rate of 10.4%. Most of the population (as of 2000[update]) speaks German (91.9%), with Italian being second most common ( 2.4%) and French being third ( 0.9%).
The age distribution, as of 2008[update], in Sisseln is; 149 children or 11.3% of the population are between 0 and 9 years old and 145 teenagers or 11.0% are between 10 and 19. Of the adult population, 142 people or 10.8% of the population are between 20 and 29 years old. 196 people or 14.9% are between 30 and 39, 252 people or 19.2% are between 40 and 49, and 199 people or 15.1% are between 50 and 59. The senior population distribution is 136 people or 10.3% of the population are between 60 and 69 years old, 65 people or 4.9% are between 70 and 79, there are 28 people or 2.1% who are between 80 and 89,and there are 3 people or 0.2% who are 90 and older.
As of 2000[update], there were 20 homes with 1 or 2 persons in the household, 248 homes with 3 or 4 persons in the household, and 241 homes with 5 or more persons in the household.As of 2000[update], there were 521 private households (homes and apartments) in the municipality, and an average of 2.4 persons per household.In 2008[update] there were 279 single family homes (or 46.4% of the total) out of a total of 601 homes and apartments. There were a total of 8 empty apartments for a 1.3% vacancy rate.As of 2007[update], the construction rate of new housing units was 8.1 new units per 1000 residents.
In Sisseln about 74.1% of the population (between age 25-64) have completed either non-mandatory upper secondary education or additional higher education (either university or a Fachhochschule). Of the school age population (in the 2008/2009 school year[update]), there are 123 students attending primary school in the municipality.
The historical population is given in the following table: