Dry period heat stress impairs dairy cows’ subsequent lactation performance. We hypothesize that exposure of late-gestation dams to dry period heat stress also exerts transgenerational effects on their daughters’ and granddaughters’ productivity. We tested this hypothesis using lactation records from previous experiments conducted during 9 summers at the University of Florida (2007–2012, 2014, 2016, and 2017, THI >68 for all years). A total of 154 multiparous dams were provided active cooling (CL_F0, shade, fans and soakers, n = 75) or shade only (HT_F0, n = 79) during a 46 d dry period. Milk yield, fat and protein records (Afimilk Ltd.) of the dams, daughters (CL_F1 n = 64, HT_F1 n = 44) and granddaughters (CL_F2 n = 24, HT_F2 n = 13) of those dams were used to estimate ECM from calving to 35 wk in milk (WIM) for 2 consecutive lactations. Data were analyzed using mix models in SAS with WIM as repeated measure and dam within treatment as random effect. Dry HT_F0 dams produced 2.3 kg less milk/d in their subsequent lactation than dry CL _F0 dams [ECM: 34.2 vs. 36.5 ± 0.07 kg, respectively; P < 0.01]. Daughters born to HT_F0 dams, who experienced heat conditions through the intrauterine environment, produced 3.7 kg less milk/d during their first lactation [ECM: 28.6 vs.. 32.3 ± 0.08 kg for HT_F1 and CL_F1, respectively; P < 0.01], and 3.4 kg/d less during their second lactation [ECM: 33.2 vs.. 36.6 ± 0.13 kg, WIM by treatment interaction; P < 0.01], compared with those born to CL_F0 dams. Similarly, the granddaughters of HT_F0 dams, born to HT_F1, produced 3.7 kg less milk/d during their first lactation [ECM: 28.5 vs.. 32.2 ± 0.13 kg for HT_F2 and CL_F2, respectively; P < 0.01] and 6.5 kg/d less in their second lactation [ECM: 34.0 vs.. 40.5 ± 0.21 kg, WIM by treatment interaction, P < 0.01] compared with granddaughters of CL_F0 dams born to CL_F1. Dry period heat stress not only impairs dam’s subsequent lactation but also has carryover effects on the productivity of daughters and granddaughters 2 generations later. Dry-period cooling is crucial to rescue milk loss of the dam, but also to prevent milk losses of their daughters and the granddaughters.