Evidence-based assessment (EBA) is foundational to high-quality mental health care for youth and is a critical component of evidence-based practice delivery, yet is underused in the community. Administration time and measure cost are barriers to use; thus, identifying and disseminating brief, free, and accessible measures are critical. This Evidence Base Update evaluates the empirical literature for brief, free, and accessible measures with psychometric support to inform research and practice with youth. A systematic review using PubMed and PsycINFO identified measures in the following domains: overall mental health, anxiety, depression, disruptive behavior, traumatic stress, disordered eating, suicidality, bipolar/mania, psychosis, and substance use. To be eligible for inclusion, measures needed to be brief (50 items or less), free, accessible, and have psychometric support for their use with youth. Eligible measures were evaluated using adapted criteria established by De Los Reyes and Langer (2018) and were classified as having excellent, good, or adequate psychometric properties. A total of 672 measures were identified; 95 (14%) met inclusion criteria. Of those, 21 (22%) were "excellent," 34 (36%) were "good," and 40 (42%) were "adequate." Few measures had support for their use to routinely monitor progress in therapy. Few measures with excellent psychometric support were identified for disordered eating, suicidality, psychosis, and substance use. Future research should evaluate existing measures for use with routine progress monitoring and ease of implementation in community settings. Measure development is needed for disordered eating, suicidality, psychosis, and substance use to increase availability of brief, free, accessible, and validated measures.