Introduction: Given recent advances in treatment, screening for hepatitis C virus (HCV) is a public health priority with a view to the potential eradication of HCV. To identify the population that could benefit from population-based screening as a complement to the current strategy of targeted screening for risk exposures, we estimated the number of adults undiagnosed with chronic hepatitis C and their distribution by sex and age group in 2004 and 2014. Methods: A model accounting for mortality, HCV incidence, and screening rates was applied to estimates from the 2004 national prevalence survey of hepatitis B and C. Results: In 2014, the number of undiagnosed adults aged 18–80 with chronic hepatitis C among the affected population was estimated at 74,102 (plausibility interval: 64,920–83,283) vs. 100,868 (95% confidence interval, [95% CI: 58,534–143,202]) in 2004. Nearly half of them were men aged 18–59 in 2014. The proportion of people undiagnosed with chronic hepatitis C in 2004 (43%) varied significantly by age, ranging from 21.9% among those born between 1945 and 1965 to 74.1% among those born between 1924 and 1944. Consequently, the demographic profiles of chronically infected individuals (both diagnosed and undiagnosed) and undiagnosed individuals differed, with those born between 1945 and 1965 accounting for 48.9% and 24.7% of these groups, respectively. Conclusions: The number of people undiagnosed with chronic hepatitis C remained high in 2014, despite a marked decrease compared to 2004. This study contributed to the development, in 2014, of a new screening recommendation consisting of simultaneously testing men aged 18 to 60 for HCV, HBV, and HIV at least once in their lifetime, regardless of exposure to risk factors. Further studies are needed to assess the cost-effectiveness and feasibility of this new strategy. This work also highlighted the need for data on individuals undiagnosed with chronic hepatitis C—whose demographic profiles differ from those of the overall population of chronically infected individuals—to help guide screening strategies.