When you ship an order with UPS Surepost, FedEx Smartpost, or DHL eCommerce the end delivery is generally done by USPS. In the industry, we call it "last-mile delivery". FedEx, UPS, or DHL get the shipment close to you or the end delivery and then they hand it off to USPS. The last mile of the delivery is a lot of times the most expensive part of the delivery.
Sometimes, you can head to https://tools.usps.com/go/TrackConfirmAction_input and search the tracking number to see where it is.
Just know, it will generally be delivered within a few days!