This study investigated the effects of word frequency, collocational frequency, L1 congruency, and L2 proficiency, on L2 collocational processing. Two groups of L1 Japanese speakers of English (intermediate and advanced) and one group of English native speakers (NSs) performed an online acceptability judgment task on four types of adjective-noun constructions: (1) congruent collocations; (2) English-only collocations; (3) Japanese-only collocations; and (4) baseline items. Response times were analyzed using mixed-effects modeling and correlations. In contrast to NSs, nonnative speakers (NNSs) processed congruent collocations significantly faster than English-only collocations. As for frequency, all three groups demonstrated sensitivity to both word-level and collocation-level frequency. However, the distributions differed across the three groups. We concluded that age/order of acquisition effects (Carroll & White, 1973) provided the best explanation for the congruency results. Regarding the frequency results, we concluded that the findings conflict with claims that NNSs may process formulaic sequences differently than NSs (e.g., Wray, 2002, 2008).