[3] Sissach has an area, of 8.87 square kilometers (3.42 sq mi).

It grew along the road between the Schafmatt and Unterer Hauenstein Jura passes.

[8] Most of the population (as of 2000[update]) speaks German (4,723 or 88.7%), with Italian language being second most common (180 or 3.4%) and Portuguese being third (98 or 1.8%).

[9] As of 2008[update], the gender distribution of the population was 49.5% male and 50.5% female.

[9] As of 2000[update], there were 2332 private households in the municipality, with an average of 2.2 persons within each.

[8] Out of a total of 2378 households that answered this question, 34.9% were made up of just one person.

The entire town of Sissach is part of the Inventory of Swiss Heritage Sites.

[8] There were 2902 residents of the municipality who were employed in some capacity, of which females made up 43.3% of the workforce.

In 2008[update] the total number of full-time equivalent jobs was 3117.

The number of jobs in the primary sector was 60, of which 52 were in agriculture and 7 were in forestry or lumber production.

The number of jobs in the secondary sector was 1431, of which 898 (62.8%) were in manufacturing, 2 (0.1%) were in mining and 516 (36.1%) were in construction.

In the tertiary sector, 526 (32.3%) were in wholesale or retail sales or the repair of motor vehicles, 53 (3.3%) were in the movement and storage of goods, 110 (6.8%) were in a hotel or restaurant, 45 (2.8%) were in the information industry, 68 (4.2%) were the insurance or financial industry, 146 (9.0%) were technical professionals or scientists, 210 (12.9%) were in education and 191 (1.7%) were in health care.

[8] From the 2000 census[update], 1270 or 23.8% were Roman Catholic, while 2,927 (55.0%) belonged to the Swiss Reformed Church.

542 (10.18%) belonged to no church, are agnostic or atheist, and 147 individuals (2.76%) did not answer the question.

The wettest month is August during which time Sissach receives an average of 122 mm (4.8 in) of precipitation.

The month with the most days of precipitation is May, with an average of 13.5, but with only 108 mm (4.3 in) of rain or snow.

The driest month of the year is February with an average of 65 mm (2.6 in) of precipitation over 11.2 days.