Olsberg has a population () of , 7.7% of the population are foreign nationals. Over the last 10 years (1997–2007) the population has changed at a rate of 7.6%. Most of the population () speaks
German(96.3%), with
French being second most common ( 1.6%) and
Italian being third ( 0.5%). The age distribution, , in Olsberg is; 23 children or 6.3% of the population are between 0 and 9 years old and 37 teenagers or 10.2% are between 10 and 19. Of the adult population, 31 people or 8.5% of the population are between 20 and 29 years old. 48 people or 13.2% are between 30 and 39, 57 people or 15.7% are between 40 and 49, and 62 people or 17.1% are between 50 and 59. The senior population distribution is 77 people or 21.2% of the population are between 60 and 69 years old, 17 people or 4.7% are between 70 and 79, there are 8 people or 2.2% who are between 80 and 89, and there are 3 people or 0.8% who are 90 and older. the average number of residents per living room was 0.54 which is about equal to the cantonal average of 0.57 per room. In this case, a room is defined as space of a housing unit of at least as normal bedrooms, dining rooms, living rooms, kitchens and habitable cellars and attics. About 76.7% of the total households were owner occupied, or in other words did not pay rent (though they may have a
mortgage or a
rent-to-own agreement). , there were 8 homes with 1 or 2 persons in the household, 48 homes with 3 or 4 persons in the household, and 73 homes with 5 or more persons in the household. There were a total of 0 empty apartments for a 0.0% vacancy rate. The historical population is given in the following table: ==Heritage sites of national significance==