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Simple Summary: Heat stress results in significant economic losses to the dairy industry. At the individual cow level, core body temperature (CBT) serves as a reliable proxy for quantifying the degree of heat stress experienced by cows. As animals adapt their behavior to cope with heat stress, this study investigated behavioral patterns in dry Holstein cows with distinct CBT during the summer months, a season known for inducing heat stress in dairy cattle. Behavioral patterns were measured through visual observations and by automated activity monitoring capturing patterns such as lying, standing, eating, activity level, and rumination. Using sensor technology tracking activity 24/7, we observed that cows classified as high-temperature (HT) exhibited higher periods of heightened activity and lower periods of inactivity prepartum and diminished rumination time postpartum than low-temperature (LT) cows. Since rumination time is a key indicator of dairy cow health, our results suggest that HT cows faced greater health challenges postpartum. We also identified many differently expressed genes (DEGs) previously associated with heat stress in immune cells from HT vs. LT cows. Collectively, our results suggest that the observed behavioral and physiological differences between HT and LT cows are linked to their distinct tolerance to heat stress. The consequences of heat stress during the dry period can extend into the postpartum period, affecting health and productivity in the subsequent lactation. We hypothesized that cows with distinct core body temperatures (CBTs) would exhibit disparate behaviors associated with different degrees of heat generation or dissipation. The primary objective was to investigate behavioral differences of dry Holstein cows (n = 50) classified as high-temperature (HT) or low-temperature (LT), based on median CBT during the summer months using visual observations and accelerometer technology. A secondary objective was to investigate the transcriptome of white blood cells (WBCs) collected from a subgroup of HT and LT cows (n = 5; per group). Minor behavior differences were observed during the visual observations (performed for a total of 16h/cow). Based on automated monitoring system (AMS) data, collected 24/7 over a period of 42 days per cow, HT cows displayed higher periods of high activity and lower periods of inactivity prepartum and diminished rumination time postpartum than LT cows. There were 16 differently expressed genes (DEGs) in WBCs of HT compared to LT cows. Several of the identified DEGs have been previously associated with heat stress. The observed trends in the AMS data indicate that CBT and patterns of activity prepartum may serve as valuable predictors for identifying dairy cows with distinct tolerance to heat stress. [ABSTRACT FROM AUTHOR]