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 2011 reveal the following:
In the middle of 2011 about 2,400 people (about 1,200 men and 1,200 women) were living in the municipality, which ranks Kostanjevica na Krki 169th among Slovene municipalities. The population density was 41 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 7.5 (in Slovenia 1.6). 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 -3.3. The sum of natural increase and net migration per 1,000 population in the municipality was positive. It was 4.1 (in Slovenia 2.6).
The mean age of people in Kostanjevica na Krki was 41.6 years, which was lower than the national average (41.8).
As in most Slovene municipalities, in Kostanjevica na Krki the number of old people was higher than the number of young people: there were 114 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 117. 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 101 children or 86% of all children aged 1–5, which was more than the national average of 76%. In the school year 2011/2012 basic school in Kostanjevica na Krki was attended by about 200 pupils, while various upper secondary schools were attended by about 90 pupils. There were 60 students and 10 graduates per 1,000 people in the municipality; in Slovenia the averages were 51 per 1,000 and 10 per 1,000, respectively.
Among people aged 15–64 (i.e. working age population) about 66% were persons in employment (i.e. persons in paid employment or self-employed persons), which is more than the national average of 58%.
The registered unemployment rate was 10.7%, which is less than the national average (11.8%). 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 33% lower than the annual average of monthly earnings for Slovenia; and net earnings about 28% lower.
Every 27th person in the municipality was receiving at least one financial social assistance. In Slovenia as a whole every 24th person received at least one financial social assistance.
In 2011, there were 433 dwellings per 1,000 population. About 70% of dwellings had at least three rooms. Average size of dwellings in the municipality was 84 m2.
Every other person in Kostanjevica na Krki had a car (50 passenger cars per 100 population); cars in this municipality were on average 9 years old.
In 2011, 330 kg of municipal waste per person was collected in Kostanjevica na Krki, which is 22 kg less than on average in Slovenia.