Municipality Postojna, which is part of the primorsko–notranjska statistical region, measures 270 km2; this ranks it 13th among Slovene municipalities.
Statistical data for 2015 reveal the following:
In the middle of 2015 about 16,050 people (about 8,050 men and 8,000 women) were living in the municipality, which ranks Postojna 33th among Slovene municipalities. The population density was 59 people per square kilometre, which was lower than the national average of 102 people per square kilometre.
The number of live births was higher than the number of deaths, which means that natural increase per 1,000 population in the municipality was positive. It was 2.1 (in Slovenia 0.4). The number of people who moved from the municipality was lower than the number of people who moved into the municipality, so net migration per 1,000 population in the municipality was positive. It was 3. The sum of natural increase and net migration per 1,000 population in the municipality was positive. It was 5.1 (in Slovenia 0.6).
The mean age of people in Postojna was 41.8 years, which was lower than the national average (42.6).
As in most Slovene municipalities, in Postojna the number of old people was higher than the number of young people: there were 105 people, aged 65 or more, per 100 people aged 0–14. This ratio shows that the value of the ageing index was lower than the national average of 123. It also shows that the mean age of people in Preddvor is growing more slowly than in Slovenia as a whole. Data by sex show that the ageing index for women was in all Slovene municipalities higher than the ageing index for men. In Postojna – as in most Slovene municipalities – more women were 65+ years old than 14 or less; for men the situation was the same.
In the school year 2015/2016 basic schools in Postojna were attended by about 1,350 pupils, while various upper secondary schools were attended by about 500 pupils. There were 40 students and 9 graduates per 1,000 people in the municipality; in Slovenia the averages were 39 per 1,000 and 9 per 1,000, respectively.
Among people aged 15–64 (i.e. working age population) about 61% were persons in employment (i.e. persons in paid employment or self–employed persons), which is more than the national average (58%).
The registered unemployment rate was 11.4%, which is less than the national average (12.3%). As in most Slovene municipalities, more women than men were unemployed.
In Postojna, average monthly gross earnings per person employed by legal persons were about 6% lower than the annual average of monthly earnings for Slovenia; and net earnings about 12% lower.
In 2015, there were 413 dwellings per 1,000 population. About 59% of dwellings had at least three rooms. Average size of dwellings in the municipality was 81 m2.
Every other person in Postojna had a car (54 passenger cars per 100 population); cars in this municipality were on average 9.7 years old.
In 2015, 369 kg of municipal waste per person was collected in Postojna, which is 54 kg more than on average in Slovenia.