Offspring size can strongly influence offspring fitness; therefore, many studies have examined environmental and maternal effects on offspring size determination. However, the relative importance of individual female identity to offspring size determination is poorly understood, despite the potential of identity or genetic effects to drive offspring size adaptation and long-term population dynamics. To address this knowledge gap, we tracked diameter, mass, and density of eggs spawned by individual female yellow perch (Perca flavescens) over four spawning years to determine the relative importance of individual identity, phenotype (maternal size), and environment (winter severity) to egg size variation. Individual identity explained significant proportions (15-30%) of variance in egg diameter and mass, but only weakly influenced egg density. Interannual effects accounted for 30 to 50% of the variation in egg characteristics, and were strongly negatively correlated to winter severity (r ≤ -0.90) for egg mass and egg density (i.e., egg mass and density increased with warmer overwinter temperatures). Our results suggest that individual effects comprise a large amount of the intrapopulation variation in egg size in fish populations which may be unaccounted for in studies examining only the effects of environment or maternal phenotype. Accounting for potential identity effects would likely improve our understanding of constraints on offspring size plasticity and potential responses of offspring size in populations experiencing environmental change.