Background: Colorado’s age-adjusted fatal opioid overdose rate increased over 400% from 2000 to 2020. Public libraries are increasingly valuable community resources for accessing health-related information. We sought to evaluate the availability and types of opioid use disorder (OUD)-related resources offered through Colorado Public Library branches using secret shoppers to collect data. Methods: This was a cross sectional study of 197 Colorado Public Libraries in 2021. Anonymous auditors posed as library patrons asking a brief standardized script about availability of OUD-related resources over the phone. We conducted descriptive analyses of the libraries contacted, the response types of OUD resources provided, and information about naloxone availability. Outcomes were compared between urban/rural and libraries within/outside the Denver Public Library (DPL) system via means comparison tests. Results: Approximately 50% of libraries were classified as urban. Most (81%) of the libraries offered a valid OUD-resource, and over half (51%) provided a referral to a treatment center offering at least one medication for OUD. Over a third (36%) of librarians referenced the statewide naloxone standing order allowing patients to obtain naloxone from a pharmacy without prescription. One in ten libraries provided at least one invalid referral resource. Libraries within the DPL system referenced Colorado’s naloxone standing order at higher rates than non-DPL libraries. Conclusions: Public libraries may benefit from the development of a standard for OUD-related resource training/education that can be distributed across the state to create a space for community members to obtain resources related to substance use.