In this study, we explored the processing of singular and plural word forms, using megastudies in French, English, and Dutch. For singulars, we observed a base frequency effect but no surface frequency effect. For plurals, the effect depended on the frequency of the word form. When the word form had a frequency above a threshold value, we observed both surface and base frequency effects; for the frequencies below the threshold, we found a base frequency effect only, suggesting full decomposition for these words. The threshold differed between the languages, suggesting that more plurals are decomposed in French than in Dutch and more in Dutch than in English. In contrast, for all languages the singular form seems to be coactivated whenever the plural form is processed. These results are interpreted in light of some of the main models of morphological processing.