The population of Indonesia was 270.20 million according to the 2020 national census, an increase from 237.64 in 2010. Indonesia is the fourth most populous country in the world. Approximately 55% of Indonesia's population resides on Java, which is the most populous island in the world.

Despite a fairly effective family planning program that has been in place since 1967, Indonesia's average population growth per year was over 1.1% for the decade ending in 2020, nearly having 13% population growth for that decade. At this rate, Indonesia's population is projected to surpass the population of the United States if the population growth is not maintained.

Indonesia has a relatively young population compared to Western nations, though it is aging as the country's birth rate has slowed and its life expectancy has increased. The median age was 30.2 years in 2017. Indonesia includes numerous ethnic, cultural and linguistic groups, some of which are related to each other. Since independence, Indonesian is the language of most written communication, education, government, and business. Many local ethnic languages are the first language of most Indonesians and are still important.