Municipality Miren - Kostanjevica, which is part of the Goriška statistical region, measures 63 km2; this ranks it 109th among Slovene municipalities.
Statistical data for 2012 reveal the following:
In the middle of 2012 about 4,800 people (about 2,400 men and 2,400 women) were living in the municipality, which ranks Miren - Kostanjevica 104th among Slovene municipalities. The population density was 77 people per square kilometre, which was lower than the national average of 101 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 1.0 (in Slovenia 1.3). The number of people who moved from the municipality was higher than the number of people who moved into the municipality, so net migration per 1,000 population in the municipality was negative. It was -4.6. The sum of natural increase and net migration per 1,000 population in the municipality was negative. It was -3.5 (in Slovenia 1.6).
The mean age of people in Miren - Kostanjevica was 43.3 years, which was higher than the national average (42).
As in most Slovene municipalities, in Miren - Kostanjevica the number of old people was higher than the number of young people: there were 134 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 Miren - Kostanjevica 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 Miren - Kostanjevica – as in most Slovene municipalities – more women were 65+ years old than 14 or less; for men the situation was the same.
Miren - Kostanjevica had 4 kindergartens. They were attended by 167 children or 69% of all children aged 1–5, which was less than the national average of 75%. In the school year 2012/2013 basic schools in Miren - Kostanjevica were attended by about 310 pupils, while various upper secondary schools were attended by about 160 pupils. There were 50 students and 12 graduates per 1,000 people in the municipality; in Slovenia the averages were 47 per 1,000 and 10 per 1,000, respectively.
Among people aged 15–64 (i.e. working age population) about 55% were persons in employment (i.e. persons in paid employment or self-employed persons), which is less than the national average of 57%.
The registered unemployment rate was 11.3%, which is less than the national average (12%). In contrast to most Slovene municipalities, more men than women were unemployed.
In Miren - Kostanjevica, average monthly gross earnings per person employed by legal persons were about 11% lower than the annual average of monthly earnings for Slovenia; and net earnings about 9% lower.
In 2012, there were 416 dwellings per 1,000 population. About 80% of dwellings had at least three rooms. Average size of dwellings in the municipality was 92 m2.
About every other person in Miren - Kostanjevica had a car (64 passenger cars per 100 population); cars in this municipality were on average 10 years old.
In 2012, 400 kg of municipal waste per person was collected in Miren - Kostanjevica, which is 73 kg more than on average in Slovenia.