Municipality Kozje, which is part of the Savinjska statistical region, measures 90 km2; this ranks it 80th among Slovene municipalities.

Statistical data for 2016 reveal the following:

In the middle of 2016 about 3,100 people (about 1,570 men and 1,530 women) were living in the municipality, which ranks Kozje 154th among Slovene municipalities. The population density was 35 people per square kilometre, which was lower than the national average 102 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 0.6 (in Slovenia 0.3). 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 -5.8. The sum of natural increase and net migration per 1,000 population in the municipality was negative. It was -5.2 (in Slovenia 0.8).

The mean age of people in Kozje was 43.3 years, which was higher than the national average (42.9).

As in most Slovene municipalities, in Kozje the number of old people was higher than the number of young people: there were 132 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 125. 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.

In the school year 2016/2017 basic schools in Kozje were attended by about 240 pupils, while various upper secondary schools were attended by about 130 pupils. There were 42 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 56% were persons in employment (i.e. persons in paid employment or self-employed persons), which is less than national average (60%).

The registered unemployment rate was 13.2%, which is more than the national average (11.2%). 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 13% lower than the annual average of monthly earnings for Slovenia; and net earnings about 10% lower.

In 2015, there were 455 dwellings per 1,000 population. About 63% of dwellings had at least three rooms. Average size of dwellings in the municipality was 82 m2.

Every other person in Kozje had a car (56 passenger cars per 100 population); cars in this municipality were on average 11 years old.

In 2016, 203 kg of municipal waste per person was collected in Kozje, which is 144 kg less than on average in Slovenia.