Municipality Kozje, which is part of the Savinjska statistical region, measures 90 km2; this ranks it 80th among Slovene municipalities.
Statistical data for 2013 reveal the following:
In the middle of 2013 about 3,150 people (about 1,600 men and 1,600 women) were living in the municipality, which ranks Kozje 151st among Slovene municipalities. The population density was 35 people per square kilometre, which was lower than the national average of 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 -7.9 (in Slovenia 0.9). 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 -11.7. The sum of natural increase and net migration per 1,000 population in the municipality was negative. It was -19.6 (in Slovenia 1.1).
The mean age of people in Kozje was 42.9 years, which was higher than the national average (42.2).
As in most Slovene municipalities, in Kozje the number of old people was higher than the number of young people: there were 131 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 119. It also shows that the mean age of people in Kozje 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 Kozje – as in most Slovene municipalities – more women were 65+ years old than 14 or less; for men the situation was the same.
Kozje had 1 kindergarten. It was attended by 85 children or 70% of all children aged 1–5, which was less than the national average of 75%. In the school year 2013/2014 basic schools in Kozje were attended by about 240 pupils, while various upper secondary schools were attended by about 130 pupils. There were 50 students and 10 graduates per 1,000 people in the municipality; in Slovenia the averages were 44 per 1,000 and 9 per 1,000, respectively.
Among people aged 15–64 (i.e. working age population) about 58% were persons in employment (i.e. persons in paid employment or self-employed persons), which is more than the national average of 57%.
The registered unemployment rate was 13.6%, which is more than the national average (13.1%). As in most Slovene municipalities, more women than men were unemployed.
In Kozje, average monthly gross earnings per person employed by legal persons were about 16% lower than the annual average of monthly earnings for Slovenia; and net earnings about 13% lower.
In 2013, there were 476 dwellings per 1,000 population. About 63% of dwellings had at least three rooms. Average size of dwellings in the municipality was 82 m2.
About every other person in Kozje had a car (53 passenger cars per 100 population); cars in this municipality were on average 11 years old.
In 2013, 169 kg of municipal waste per person was collected in Kozje, which is 151 kg less than on average in Slovenia.