Background: Suicide is the second leading cause of death among youth aged 10-24 years in Washington State. Population-based data on suicidality among sexually and gender diverse (SGD) youth and modifiable protective factors from Washington are limited. Methods: Using data from the 2021 Washington Healthy Youth Survey, a statewide, population-based, cross-sectional survey among 8th-12th graders, we compared suicidality (suicide ideation, planning, and attempt) among SGD youth with heterosexual, cisgender youth. Prevalence ratios (PRs) adjusted for grade and urban-rural status were used to assess family, school, and community protective factors of suicidality among SGD youth. Results: Of 121,401 included students, 34,635 (28.5%) identified as SGD. Among SGD youth, 41.2% reported suicidal ideation, 32.8% reported suicide planning, and 17.8% reported a suicide attempt during the past year, 3.3-3.8 times higher than heterosexual, cisgender respondents. Having opportunities for school involvement (PR: 0.54; 95% CI: 0.53-0.55) and feeling safe at school (PR: 0.59; 95% CI: 0.58-0.60) were associated with the lowest relative prevalence of suicidal ideation among SGD youth. Implications for School Health Policy, Practice, and Equity: Interventions that engage adults to establish safe and supportive environments might help to prevent suicidality among SGD youth. Conclusions: Many Washington 8th, 10th, and 12th graders identified as SGD, and these youth experienced a substantial, disproportionate prevalence of suicidality Multiple family, school, and community protective factors were associated with lower suicidality among SGD youth and could be helpful points of intervention for statewide youth suicidality programs.