Attention-deficit/hyperactivity disorder (ADHD) is a prevalent, persistent, and costly mental health condition. The internet is an increasingly popular source for information related to ADHD. With a nationally representative sample (2018 NSCH), we aimed to separate individual- and state-level effects to examine inequities in ADHD diagnoses. We extracted state-level relative search volumes using "ADHD," "ADHD treatment," "ADHD medication," and "ADHD therapy" from Google Trends, and sociodemographic and clinical variables from the 2018 National Survey of Children's Health (N = 26,835). We examined state variation in ADHD-related information-seeking and applied multilevel modeling to examine associations among individual-level race/ethnicity, state-level information-seeking patterns, and ADHD diagnoses. Online information seeking related to ADHD varies by state and search term. Individual-level racial/ethnic background and state-level information-seeking patterns were associated with ADHD diagnoses; however, their cross-level interaction was not significant. This study adds to the strong body of evidence documenting geographical variation and diagnostic disparity in mental health and the growing literature on the impact of the digital divide on population health, indicating an urgent need for addressing inequities in mental health care. Increasing public interest in and access to empirically supported online information may increase access to care, especially among people of color.