This study investigates two types of covered piglet creep boxes in a naturally ventilated swine farrowing building with regards to air quality (ammonia and carbon dioxide levels), piglet usage of the box, and piglet health and performance. The covered creep boxes featured either double plastic curtains along the entire width of the box (designated as the DC box) or an arc-shaped access opening occupying about one-third of the box width (designated as the AO box). The study was conducted with 12 farrowing crates, six per box regimen, during wintertime. Continuous, 24-h video observations of the piglet behaviors were made at days 2, 9, and 16 of post-parturition. Ammonia and CO2 concentrations inside the creep boxes were measured using portable electronic sensors. The results showed that the interior NH3 levels tended to be lower for the DC type than for the AO type, although the magnitude was quite low in both cases (averaging 4 to 6 ppm). No significant difference was found in the interior CO2 concentrations between the two box types. Pre-weaning piglet culling rate (mean±S.D.) was 2.5±0.08% and 11.3±1.17% for the DC and AO litters, respectively (p < 0.001). Although there was no significant treatment effect (p = 0.26), piglet diarrhea morbidity was numerically lower for the DC litters (0.80±0.03%) than for the AO litters (1.29±0.12%). At 21-d weaning age, the DC litters showed heavier body weight (6.18±0.23 kg) than the AO litters (5.69±0.18 kg) (p < 0.05). Results of the present work, despite the relatively small sample size, indicate that the DC-style covered creep box seems more conducive to enhancing piglet usage of the box and piglet health and performance.