The Census of population, households and apartments in the Republic of Croatia in 2021 (Croatian: Popis stanovništva, kućanstva i stanova u Republici Hrvatskoj 2021. godine; shortened: Census 2021, Popis 2021.) was the 4th decennial Croatian census. Census Day, the reference day used for the census, was August 31, 2021. This was the first Croatian census to offer options to online self-numeration, in addition to the paper response form used for previous censuses. The census was taken during the COVID-19 pandemic, which affected its administration. The census recorded a resident population of 3,871,833 in the twenty counties and the City of Zagreb, a decrease of 9.64 percent, or 413,056 over the preceding decade. The fall rate was the biggest ever recorded. Questions and data uses The Census collects the following data: Population surname and first name, gender, personal identification number (PIN), date of birth, marital status; the type of living community in which a person lives; number of live births; place of residence/residence; presence in the census settlement at the time of the Census; reason for absence/presence; time of absence/presence; time of intention of absence/presence; place of absence/place of residence; birthplace; place of residence of the mother at the time of the person's birth; the place from which the person immigrated and the year and reason for immigrating; the foreign country where the person resided for a year or longer, the year of moving to the Republic of Croatia and the reason for staying abroad; citizenship; nationality (national affiliation); mother tongue; religious affiliation; achieved education; attending school/studies; economic activity, position in employment; interest; activities; main sources of livelihood; place of work/school; frequency of returning to the place of residence; means of travel to work/school/study Households relative and family composition of the household; type of household; the basis on which the household uses the apartment; area of used agricultural land and ownership of livestock or poultry Housing and other residential units type and manner of use of the residential unit; apartment ownership; surface area of the apartment; number of rooms in the apartment; kitchen, bathroom and toilet in the apartment; types of installations in the apartment (water supply, sewage, electricity, gas installations); method of heating the apartment; type of energy source; air conditioning; type of building in which the apartment is located; the number of apartments in the building where the apartment is located, the location of the apartment in the building;