Municipality Kostanjevica na Krki, which is part of the Posavska statistical region, measures 58 km2; this ranks it 119th among Slovene municipalities.
Statistical data for 2016 reveal the following:
In the middle of 2016 about 2,410 people (about 1,210 men and 1,210 women) were living in the municipality, which ranks Kostanjevica na Krki 170th among Slovene municipalities. The population density was 41 people per square kilometre, which was lower than the national average 102 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 municipality was negative. It was -0.8 (in Slovenia 0.3). 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 3.3. The sum of natural increase and net migration per 1,000 population in the municipality was positive. It was 2.5 (in Slovenia 0.8).
The mean age of people in Kostanjevica na Krki was 42.7 years, which was lower than the national average (42.9).
As in most Slovene municipalities, in Kostanjevica na Krki the number of old people was higher than the number of young people: there were 115 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 125. 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 – in contrast to most Slovene municipalities – more women were 65+ years old than 14 or less; for men the situation was exactly the opposite.
In the school year 2016/2017 basic school in Kostanjevica na Krki was attended by about 220 pupils, while various upper secondary schools were attended by about 90 pupils. There were 39 students and 14 graduates per 1,000 people in the municipality; in Slovenia the averages were 39 per 1,000 and 15 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 national average (60%).
The registered unemployment rate was 10.2%, which is less than the national average (11.2%). In contrast to most Slovene municipalities, more men than women were unemployed.
In Kostanjevica na Krki, average monthly gross earnings per person employed by legal persons were about 31% lower than the annual average of monthly earnings for Slovenia; and net earnings about 27% lower.
In 2015, there were 415 dwellings per 1,000 population. About 71% of dwellings had at least three rooms. Average size of dwellings in the municipality was 85 m2.
Every other person in Kostanjevica na Krki had a car (58 passenger cars per 100 population); cars in this municipality were on average 11 years old.
In 2016, 344 kg of municipal waste per person was collected in Kostanjevica na Krki, which is 3 kg less than on average in Slovenia.