Municipality Mirna Peč, which is part of the Jugovzhodna Slovenija statistical region, measures 48 km2; this ranks it 137th among Slovene municipalities.

Statistical data for 2020 reveal the following:

In the middle of 2020 about 3,020 people (about 1,540 men and 1,480 women) were living in the municipality, which ranks Mirna Peč 154th among Slovene municipalities. The population density was 63 people per square kilometre, which was lower than the national average of 104 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 2.0 (in Slovenia -2.5). 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 14.9. The sum of natural increase and net migration per 1,000 population in the municipality was positive. It was 16.9 (in Slovenia 6.2).

The mean age of people in Mirna Peč was 41.2 years, which was lower than the national average (43.6).

In contrast to most Slovene municipalities, in Mirna Peč the number of young people was higher than the number of old people: there were 88 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 136. It also shows that the mean age of people in Mirna Peč is growing more slowly than in Slovenia as a whole. Data by sex show that the ageing index for women was in all municipalities except in three (Dobrovnik/Dobronak, Jezersko in Loški Potok) higher than the ageing index for men. In Mirna Peč – as in most Slovene municipalities – more women were 65+ years old than 14 or less; for men the situation was exactly the opposite.

Mirna Peč had 1 kindergarten, which was attended by 181 children. Of all children in the municipality aged 1–5, 69% were included in kindergartens, which was less than national average of 81%. In the school year 2020/21 elementary school in Mirna Peč was attended by about 350 pupils, while various upper secondary schools were attended by about 110 pupils. There were 45 students and 12 graduates per 1,000 people in the municipality; in Slovenia the averages were 39 per 1,000 and 7 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 (66%).

In Mirna Peč, average monthly gross earnings per person employed by legal persons were about 11% lower than the annual average of monthly earnings for Slovenia; net earnings were about 10% lower.

Among 1,000 inhabitants in the municipality, 597 had a passenger car. The car was on average 10 years old.

In 2020, 242 kg of municipal waste per person was collected in Mirna Peč, which is 113 kg less than on average in Slovenia.