To determine the prevalence of genital Chlamydia trachomatis (chlamydia) infection, knowledge about chlamydia and experience of previous testing for chlamydia, we carried out a national probability-based survey in emerging adults aged 18-25 years in Croatia in 2021-2022. Participants (n = 1197), members of a national online panel, completed a web-based questionnaire that collected information on socio-demographics, sexual behaviours and knowledge about sexually transmitted infections (STIs). Urine specimens from a sample of sexually experienced participants were self-collected and tested for chlamydia using Cobas 4800 CT/NG test. To achieve broad representativeness of the emerging adult population in the country, we applied post-hoc weighting for gender and age. Multivariable ordinary least squares linear regression was used to determine correlates of knowledge about chlamydia infection and binomial logistic regression to assess correlates of the willingness to test for chlamydia. Among 448 participants who sent in their urine specimens chlamydia prevalence was 2.5% (95% CI 1.2-5.1) in women and 1.0% (0.3-3.2%) in men. A total of 8.0% of women and 4.7% men reported testing for chlamydia prior to the survey. About a quarter of the sample was characterized by not answering correctly any of the six questions related to knowledge about chlamydia, while only 9.6% had five or six correct answers. In the multivariable analysis, significantly higher odds of willingness to test for chlamydia were found in females compared to males (OR = 1.34, p = 0.024), those with better knowledge about the infection (OR = 1.11, p = 0.005), and those with lower religiosity (OR = 0.91, p = 0.017). In conclusion, prevalence of chlamydia in emerging adults in Croatia is considerable. Efforts to control this infection should focus on primary prevention and targeted testing combined with effective case management strategies.