Differences between languages in count (e.g., cup) and mass (e.g., rice) nouns have been shown to impact cognition, but few studies have directly examined how the morphology associated with count and mass constructions is acquired and linked to differences in meaning. Two experiments examined the relation between English and Spanish plural morphology and the interpretation of nouns as individuated objects. In Experiment 1, English- and Spanish-speaking children and adults participated in two tasks. One task examined how participants produced plurals for nouns. Results from this task indicated that both language groups make a distinction in their use of plural morphology for count and mass nouns between 5 and 7 years of age. However, that morphological distinction was stronger and occurred earlier among English speakers. A second task examined whether the count (but not the mass) nouns in each language denoted individuated objects. Speakers of both languages tended to treat all nouns as referring to individuated objects at 5 years of age. Beginning at 7 years of age, English speakers made a reliable distinction between the referents of mass and count nouns. Speakers of Spanish however, treated both types of nouns as referring to individuated objects in this task throughout development. Experiment 2 examined the interpretation of nouns by adult speakers of both languages using a different task, and the results offer converging evidence that Spanish speakers are more likely than English speakers.