Introduction: There are a limited number of epidemiological studies describing the global burden of chronic diffuse interstitial lung diseases (ILD) and their subtypes’ heterogeneity worldwide. Our main is to characterize new-onset ILDs in Algeria and compare our results with data from other populations. Materials and Methods: Newly diagnosed ILDs were prospectively collected in a single-center observational cohort study including all patients diagnosed as ILDs in the pulmonology, phthisiology, and allergology departments between 2015 and 2019. Detailed anamnestic and clinical data were collected at the time of diagnosis. The results of high-resolution computed tomography (HRCT), serological tests, biology data, and respiratory functional exploration were systematically performed and collected. Results: A total of 455 cases were included. The mean age was 59.4 ± 13.2 years. There was a slight predominance of females (300; 65.9%). The most common disease was ILD secondary to connective tissue disease (CTD) or ILD-CTD (48.1%), followed by idiopathic interstitial pneumonias (IIPs) (23.5%), sarcoidosis (16.9%), interstitial pneumonia with autoimmune features (IPAF) (12.1%), and hypersensitivity pneumonitis (HP) (2.4%). Idiopathic pulmonary fibrosis (IPF) was present in 8.6% and unclassifiable ILD in 4.6% of the total ILD cases. Conclusions: ILD-CTD, IIP, and sarcoidosis were the most frequently observed ILDs in this Algerian population. Similarities and many differences were found compared to previous data from other countries.