Transgender and nonbinary (TGNB) people face discrimination based on negative societal attitudes toward TGNB identities. Our study explored factors contributing to negative TGNB attitudes, including participants’ gender, age, religion, right-wing authoritarianism (RWA), social dominance orientation (SDO), and adherence to traditional gender ideologies. Our sample of 808 U.S. Mechanical Turk participants completed measures of RWA, SDO, traditional masculinity and femininity, and transgender attitudes and beliefs. Because TGNB people have diverse identities, we modified the transgender attitudes and beliefs scale to measure attitudes toward trans man, trans woman, and nonbinary targets instead of the single “transgender” umbrella. Results of multiple regression analyses indicated that gender was a significant predictor of attitudes toward trans men and trans women. Higher levels of RWA, traditional masculinity, and anti-egalitarianism (a domain of SDO) predicted negative attitudes toward all TGNB identities, with RWA generally being the strongest predictor. Traditional femininity and the dominance domain of SDO did not significantly contribute to our predictive model for most groups, although we were surprised to find that for nonbinary people, higher levels of traditional femininity predicted positive attitudes. These results can inform targeted interventions aimed at reducing transprejudice.