Municipality Sežana, which is part of the Obalno-kraška statistical region, measures 217 km2; this ranks it 25th among Slovene municipalities.
Statistical data for 2009 reveal the following:
In the middle of 2009 about 12,800 people (about 6,500 men and 6,300 women) were living in the municipality, which ranks Sežana 42nd among Slovene municipalities. The population density was 59 people per square kilometre, which was lower than the national average of 101 people per square kilometre.
The number of live births was lower than the number of deaths, which means that natural increase per 1,000 population in the muncipality was negative. It was -2.7 (in Slovenia 1.5). 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 23.5. The sum of natural increase and net migration per 1,000 population in the municipality was positive. It was 20.8 (in Slovenia 7.2).
The mean age of people in Sežana was 43.1 years, which was higher than the national average (41.4 years).
As in most Slovene municipalities, in Sežana the number of old people was higher than the number of young people: there were 143 people, aged 65 or more, per 100 people aged 0–14. This ratio shows that the value of the ageing index was higher than the national average of 118. It also shows that the mean age of people in Sežana is growing more rapidly 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 Sežana – as in most Slovene municipalities – more women were 65+ years old than 14 or less; for men the situation was the same.
Sežana had 6 kindergartens. They were attended by 404 children or 71% of all children aged 1–5, which was less than the national average of 72%. In the school year 2009/10 elementary schools in Sežana were attended by about 860 pupils, while various upper secondary schools were attended by about 430 pupils. There were 60 students and 9 graduates per 1,000 people in the municipality; in Slovenia the averages were 56 per 1,000 and 9 per 1,000, respectively.
Among people aged 15–64 (i.e. working age population) about 64% were persons in employment (i.e. persons in paid employment or self-employed persons), which is more than the national average of 61%.
The registered unemployment rate was 5.3%, which is less than the national average (9.1%). As in most Slovene municipalities, more women than men were unemployed.
In Sežana, average monthly gross earnings per person employed by legal persons were about 5% lower than the annual average of monthly earnings for Slovenia; and net earnings about 4% lower.
Every 31st person in the municipality was receiving at least one financial social assistance. In Slovenia as a whole every 23rd person received at least one financial social assistance.
The value of gross investment in new fixed assets in the municipality (EUR 2,780 per capita) was higher than the national average (EUR 2,564 per capita).
In 2009, there were 418 dwellings per 1,000 population. About 72% of dwellings had at least three rooms. Average size of dwellings in the municipality was 86 m2.
About every other person in Sežana had a car (59 passenger cars per 100 population); cars in this municipality were on average 8 years old.
In tourist accommodations in the municipality around 42,800 arrivals and 64,100 overnight stays of tourist were recorded, which is approximately 1.4% of all arrivals and 0.7% of all overnight stays of tourists in Slovenia.
In 2009, 460 kg of municipal waste per person was collected in Sežana, which is 56 kg more than on average in Slovenia.