The rate of HIV infection among young Black men who have sex with men (YBMSM) aged 16-29 is increasing significantly in the United States. Prevention in this population would considerably impact future health-care resources given the need for lifelong antiretrovirals. A YBMSM population estimate is needed to assist HIV prevention program planning. This analysis estimates the number of YBMSM aged 16-29 living on the south side of Chicago (SSC), the Chicago HIV epicenter, as the first step in eliminating HIV in this population. Three methods were utilized to estimate the number of YBMSM in the SSC. First, an indirect approach following the formula a = k/b; where a = the estimated number of YBMSM, k = the average YBMSM HIV prevalence estimate, and b = the YBMSM population-based HIV seropositivity rate. Second, data from the most recent National Survey of Family Growth (NSFG) was used to estimate the proportion of Black men who report having sex with a man. Third, a modified Delphi approach was used, which averaged community expert estimates. The indirect approach yielded an average estimate of 11.7 % YBMSM, the NSFG yielded a 4.2 % (95 % CI 2.28-6.21) estimate, and the modified Delphi approach yielded estimates of 3.0 % (2.3-3.6), 16.8 % (14.5-19.1), and 25 % (22.0-27.0); an average of 14.9 %. The crude average of the three methods was 10.2 %. Applied to SSC, this results to 5,578 YBMSM. The estimate of 5,578 YBMSM represents a group that can be feasibly reached with HIV prevention efforts. Population estimates of those most at risk for HIV will help public health officials allocate resources, offering potential for elimination of new HIV cases.