Lengnau has a population (as of December 2018) of 5,254.
 As of 2010, 18.9% of the population are resident foreign nationals.
 Over the last 10 years (2000-2010) the population has changed at a rate of 2.3%.
 Migration accounted for 6%, while births and deaths accounted for -2.9%.

Most of the population (as of 2000) speaks German (3,914 or 87.8%) as their first language, French is the second most common (116 or 2.6%) and Italian is the third (103 or 2.3%).
 There are 3 people who speak Romansh.

As of 2008, the population was 48.8% male and 51.2% female.
 The population was made up of 1,778 Swiss men (38.6% of the population) and 467 (10.1%) non-Swiss men.
 There were 1,953 Swiss women (42.4%) and 40 (0.9%) non-Swiss women.
 Of the population in the municipality, 1,383 or about 31.0% were born in Lengnau and lived there in 2000.
 There were 1,195 or 26.8% who were born in the same canton, while 1,009 or 22.6% were born somewhere else in Switzerland, and 713 or 16.0% were born outside of Switzerland.

As of 2010, children and teenagers (0–19 years old) make up 18.9% of the population, while adults (20–64 years old) make up 59.7% and seniors (over 64 years old) make up 21.4%.

As of 2000, there were 1,565 people who were single and never married in the municipality.
 There were 2,319 married individuals, 298 widows or widowers and 277 individuals who are divorced.

As of 2000, there were 612 households that consist of only one person and 97 households with five or more people.
 In 2000, a total of 1,936 apartments (89.6% of the total) were permanently occupied, while 86 apartments (4.0%) were seasonally occupied and 138 apartments (6.4%) were empty.
 As of 2010, the construction rate of new housing units was 1.1 new units per 1000 residents.
 The vacancy rate for the municipality, in 2011, was 1.96%.

The historical population is given in the following chart:
Lengnau has a population (as of December 2018) of 5,254.  As of 2010, 18.9% of the population are resident foreign nationals.  Over the last 10 years (2000-2010) the population has changed at a rate of 2.3%.  Migration accounted for 6%, while births and deaths accounted for -2.9%.
Most of the population (as of 2000) speaks German (3,914 or 87.8%) as their first language, French is the second most common (116 or 2.6%) and Italian is the third (103 or 2.3%).  There are 3 people who speak Romansh.
As of 2008, the population was 48.8% male and 51.2% female.  The population was made up of 1,778 Swiss men (38.6% of the population) and 467 (10.1%) non-Swiss men.  There were 1,953 Swiss women (42.4%) and 40 (0.9%) non-Swiss women.  Of the population in the municipality, 1,383 or about 31.0% were born in Lengnau and lived there in 2000.  There were 1,195 or 26.8% who were born in the same canton, while 1,009 or 22.6% were born somewhere else in Switzerland, and 713 or 16.0% were born outside of Switzerland.
As of 2010, children and teenagers (0–19 years old) make up 18.9% of the population, while adults (20–64 years old) make up 59.7% and seniors (over 64 years old) make up 21.4%.
As of 2000, there were 1,565 people who were single and never married in the municipality.  There were 2,319 married individuals, 298 widows or widowers and 277 individuals who are divorced.
As of 2000, there were 612 households that consist of only one person and 97 households with five or more people.  In 2000, a total of 1,936 apartments (89.6% of the total) were permanently occupied, while 86 apartments (4.0%) were seasonally occupied and 138 apartments (6.4%) were empty.  As of 2010, the construction rate of new housing units was 1.1 new units per 1000 residents.  The vacancy rate for the municipality, in 2011, was 1.96%.
The historical population is given in the following chart:
Lengnau, Bern