Ground transport of pigs at early ages may result in profit-stripping incidences of mortality and compromised animal welfare due to stress stemming from unfavorable transport conditions. The objective of this study was to examine possible causative relationships of mortality rate of weaned and feeder pigs to ground transport conditions. A total of 7056 transportation records of weaned pigs (3174 records) and feeder pigs (3882 records) for the period from April 2012 to January 2014 were provided by a U.S. swine company. Effects of pig type (weaned vs. feeder pigs), ambient temperature (25°C or warm/hot), travel distance (<600 >km, 600 to 900 km, 900 to 1200 km, 1200 to 1500 km, and >1500 km), and the interactive effects on dead-on-arrival (DOA) rate (DOA per head loaded, %) were evaluated. The effects of the same variables on post-transport mortality of weaned pigs were also evaluated. Results show that DOA rate was affected by pig type, ambient temperature, and travel distance interactively. Weaned pig DOA rates (mean ±SE of 0.0333% ±0.0150%) tended to be higher than feeder pig DOA rates (0.0243% ±0.0110%) (p = 0.0004), and weaned pigs were more vulnerable to transport stress in warm/hot conditions. For weaned pigs, DOA rates were higher with >900 km travel distance (0.0543% ±0.0389%) than with(0.0118% ±0.0078%) in cool/cold conditions, and DOA rates significantly increased as travel distance increased in warm/hot conditions. For feeder pigs, DOA rates were not affected by travel distance in cool/cold or mild conditions; however, higher mortality rates were found with >1200 km travel distance (0.2717% ±0.1326%) than with(0.0315% ±0.0151%) in warm/hot conditions. Statistical analysis showed that post-transport mortality rate of weaned pigs was affected by ambient temperature during transport and travel distance interactively for the first one or two weeks after transport. However, it should be noted that the relationship between post-transport mortality and transport conditions could have been confounded by other factors, such as management at the finishing farm. Outcomes of this study are expected to offer insight into improving the ground transport of pigs.