usps overnight packages are sent through the USPS Priority Mail Express service, which guarantees overnight delivery to most U.S. locations. This service is the fastest offered by the United States Postal Service, ensuring that packages are delivered by 10:30 AM the next day in most cases. USPS overnight packages come with tracking and are insured for up to $100 against loss or damage. The cost of sending an overnight package through USPS depends on the size and weight of the package, as well as the destination. For smaller items, flat-rate boxes are available, which can offer more predictable pricing. Larger or heavier packages will be subject to weight-based rates. USPS offers competitive pricing for overnight shipments, making it an attractive option for businesses and individuals who need to send urgent packages across the country. Although other carriers like UPS and FedEx also provide overnight shipping, USPS is often the most economical choice for smaller items.