Abstract Michigan has a long history of adverse environmental exposures, many of which are still ongoing, like the Flint water crisis, extreme air pollution burden, and widespread PFAS exposure. Michigan is also home to a diverse population of Latinx, Black, White, and Middle Eastern/North African (MENA) Americans. Because minority populations are underrepresented in environment and cancer research despite being at greater risk of being exposed to environmental hazards and having worse cancer outcomes, Michigan is uniquely positioned for studying the associations between environmental exposures and cancer risk. In June 2022, the Michigan Cancer and Research on the Environment Study (MI-CARES) began recruitment with a goal of establishing a cohort of over 100,000 Michiganders to examine these associations. Any Michigander aged 18-49 is eligible to enroll in MI-CARES. By focusing on this age range, we will capture exposures during important windows of susceptibility prior to the onset of most cancers.While recruitment is open to all state-wide, efforts are focused on six environmental injustice hotspots, identified using the MiEJScreen tool, a relative summary score capturing pollution burden and population vulnerability: the metro areas of Kalamazoo, Grand Rapids, Flint, Lansing, Detroit, and Bay City-Saginaw.MI-CARES will enroll equal numbers of Black, Latinx, MENA, and White participants. To support participation in diverse communities, study materials are available in Arabic, English, and Spanish. MI-CARES has employed a multifaceted community engagement strategy and is recruiting from these communities directly and with the help of community partners. An incentive of $10 is also provided to participants who successfully complete the questionnaire.To democratize participation, MI-CARES enrollment can be completely remote, but in-person and paper-based enrollment is available. Enrollment includes a baseline questionnaire, consent for data linkage, and annual follow-up surveys. Participants are also asked to provide saliva and blood spot samples via a mailed at-home biospecimen collection kit. Biospecimens will be analyzed for environmental exposures like heavy metals and for intermediate cancer markers including inflammation, cellular aging, immune function, and altered metabolism. Participant data will be linked to neighborhood-level exposure databases, administrative databases like cancer registries and death indices, and to the Michigan Neonatal Biobank. More than 4,000 Michiganders have enrolled in MI-CARES. Data on initial cohort members including environmental exposure history and demographic characteristics will be presented. MI-CARES is part of the Cohorts for Environmental Exposures and Cancer Risk (CEECR) consortium, which is funded by the National Cancer Institute and the National Institute for Environmental Health Sciences. Citation Format: Lilah Khoja, Maxwell Salvatore, Minh Tung Phung, Isabella De Sa, Heatherlun Uphold, Justin Colacino, Alison M. Mondul, Bhramar Mukherjee, Dana Dolinoy, Celeste Leigh Pearce. Michigan cancer and research on the environment study (MI-CARES) cohort: Baseline methods and participant characteristics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 830.