Municipality Kostanjevica na Krki, which is part of the Spodnjeposavska statistical region, measures 58 km2; this ranks it 119th among Slovene municipalities.
Statistical data for 2008 reveal the following:
At the end of 2008 about 2,400 people (about 1,200 men and 1,200 women) were living in the municipality, which ranks Kostanjevica na Krki 168th among Slovene municipalities. The population density was 41 people per square kilometre, which was lower than the national average of 100 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 0.8 (in Slovenia 1.7). 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 -4.1. The sum of natural increase and net migration per 1,000 population in the municipality was negative. It was -3.3 (in Slovenia 10.9).
The mean age of people in Kostanjevica na Krki was 41.1 years, which was lower than the national average (41.3 years).
As in most Slovene municipalities, in Kostanjevica na Krki the number of old people was higher than the number of young people: there were 117 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 118. It also shows that the mean age of people in Kostanjevica na Krki 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 Kostanjevica na Krki – as in most Slovene municipalities – more women were 65+ years old than 14 or less; for men the situation was exactly the opposite.
Kostanjevica na Krki had 1 kindergarten. It was attended by 83 children. Of all children aged 1–5, 78% were included in kindergartens, which was more than the national average of 70%. In the school year 2008/09 elementary school in Kostanjevica na Krki was attended by about 190 pupils. About 120 pupils from the municipality attended various secondary schools. There were 60 students and 6 graduates per 1,000 people in the municipality; in Slovenia the averages were 55 per 1,000 and 8 per 1,000, respectively.
Among people aged 15–64 (i.e. working age population) about 69% were persons in employment (i.e. persons in paid employment or self-employed persons), which is more than the national average of 62%.
The registered unemployment rate was 5.8%, which is less than the national average (6.7%). As in most Slovene municipalities, more women than men were unemployed.
In Kostanjevica na Krki, average monthly gross earnings per person employed by legal persons were about 40% lower than the annual average of monthly earnings for Slovenia; and net earnings about 35% lower.
Every 24th person in the municipality was receiving at least one financial social assistance. In Slovenia as a whole every 28th person received at least one financial social assistance.
The value of gross investment in new fixed assets in the municipality (EUR 606 per capita) was lower than the national average (EUR 3,165 EUR per capita).
In 2008, there were 400 dwellings per 1,000 population. About 58% of dwellings had at least three rooms. Average size of dwellings in the municipality was 78 m2.
Every fourth person in Kostanjevica na Krki had a car (25 passenger cars per 100 population); cars in this municipality were on average 8 years old.
In 2008, 306 kg of municipal waste per person was collected in Kostanjevica na Krki, which is 113 kg less than on average in Slovenia.