Human mpox has been an increasing concern in the United States and California since late 2022. While the Jynneos vaccine offers a degree of cross-protection against the disease, vaccine hesitancy is common among those recommended for vaccination. The purpose of this study was to assess vaccine knowledge, facilitators, and barriers to vaccine uptake among individuals previously diagnosed with mpox, or mpox cases, in Santa Clara County, California. In-depth interviews were conducted by public health department staff among mpox cases diagnosed in Santa Clara County between July and September 2022. Responses were analyzed using a grounded theory data analysis approach. Among the 47 participants, 36 (77%) had heard of mpox before diagnosis, and of these, 20 (56%) did not think they were at risk of developing mpox, and 28 (78%) were aware that a vaccine was available. Those who did not receive the vaccine stated vaccine access and availability were the main barriers. Among the six participants not interested in the vaccine, the main hesitancies were lack of perceived risk, stigma of being branded by scarring and labeled gay, and vaccine safety. Overall, the following themes were attributed to reasons for vaccine hesitancy: (a) lack of awareness of the disease and vaccine, including perceived risks; (b) lack of vaccine availability and accessibility; and (c) stigma associated with receiving the vaccine, including being publicly labeled as "gay" and the scarring on forearm potentially seen as branding. We recommend tailoring outreach and educational campaigns to address reasons for mpox vaccine hesitancy.