Identifying ontogenetic shifts in habitat use by aquatic organisms is necessary for improving conservation strategies; however, our ability to designate life stages based on surrogate metrics (i.e., length) is questionable without validation. This study identified growth patterns of age-0 western painted crayfish Orconectes palmeri longimanus (Faxon, 1898) reared in the laboratory, provided support for field-based designations of age-0 lengths, and identified microhabitat factors important to adult and juvenile presence from field collections. Two growth periods of a laboratory crayfish population were described using a broken line model: a rapid, early-growth period (weeks 2-20, slope = 0.81 ± 0.03SE), and a slower, late-growth period (weeks 22-50, slope = 0.13 ± 0.03SE). A smoothed curve was generated to represent the size distribution of juveniles from our laboratory population to determine the probability that an age-0 crayfish from our laboratory population had a carapace length (CL) similar to that found in previous field studies using onset of maturity (22.4 mm CL). We determined that the probability of the age-0 crayfish in our summer laboratory population exceeding 22.4 mm CL was 0.06. The threshold between the lower 0.95 and upper 0.05 probabilities was 22.9 mm CL, confirming previous field observations of onset at maturity. We used this threshold to identify juveniles and adults from our field collections, and found that both life stages were positively associated with coarse substrate and negatively associated with water depth. Adults, however, were negatively related to gravel, whereas juveniles showed a positive relationship. This result is reflective of the relationship between crayfish body size and refuge use within the interstitial spaces of substrates, whereby adult crayfish are unable to seek refuge in the small interstitial spaces of gravel.