After starting in selected cities around the country, Amazon and the U.S. Postal Service are closer to rolling out Sunday parcel delivery on a nationwide scale.

In recent weeks, Sunday delivery has launched in Seattle and Portland, and various other cities are potentially only weeks from going live — including the Boston area and a huge swath of California, including San Francisco and Silicon Valley.

GeekWire made dozens of phone calls to post offices across the country to confirm that the service is coming soon, in an apparent push that puts the rollout ahead of expectations. Separately, the U.S. Postal Service provided an updated list of markets where Sunday delivery is provided. Although incomplete, it includes other surprising areas of coverage, such a San Diego and Washington, D.C. (the full list can be found below).

In May, Amazon said 15 cities were eligible for Sunday delivery in addition to Los Angeles and the New York metro areas, where the service first launched in November 2013.

But letter carriers in two cities that were not on that list — Seattle and Portland — have been actively delivering packages for the past two Sundays. The Seattle district includes a vast area, spanning from the Canadian boarder in Blaine, Wash. to the state capitol in Olympia, according to one source. Carriers in these areas have been spotted working on Sunday and holidays, including the Fourth of July just last week.

In California, postal carriers are gearing up to start Sunday delivery for a huge district, as well. One postal carrier said the territory stretched from Eureka, Calif. to Sunnyvale, Calif., and three confirmed the service was aiming to launch as soon as the end of the month, although two others said the launch could still be six to eight weeks out.

That area includes the Bay Area, which can otherwise be called the mecca for speedy delivery. Several tech companies there are testing ways to get items delivered within hours of pressing the buy button online.

A Boston postal worker said the launch will occur there in October, but that’s not the case everywhere. A worker in Boise, Idaho said a launch is nowhere on their roadmap, as far as he is aware.

For now, Amazon is the only one tapping the U.S. Postal Service for delivering on Sundays and holidays — two times when carriers traditionally have never worked. Other companies, like eBay and Google, have experimented with building their own fleets of drivers, and a host of other startups have focused on building out a crowd-sourced delivery system.

Amazon has rolled out its grocery delivery service, Amazon Fresh, in San Francisco, in addition to Los Angeles and Seattle. It also delivers on Sunday.

An Amazon spokeswoman did not return emails sent last week asking about expanded delivery, and the U.S. Postal Service said the spokesperson knowledgeable about the matter was out until July 15 and not available.

Update: A U.S. Postal Service spokesman was able to provide GeekWire a partial list of cities where the service is live. He cautioned that he doesn’t have access to specific locations at this time, and not all addresses within these markets will automatically be served. The cities he can confirm are: Long Island, NY; New York City; Northern New Jersey; Westchester, NY; Los Angeles; San Diego; Fort Worth, Dallas and Houston in Texas; Richmond, Va.; Washington, D.C. (plus Virginia suburbs); and Seattle.

Previously, Amazon and the U.S. Postal Service said they would continue to roll out Sunday delivery to a large portion of the U.S. this year. To participate, Amazon customers can add items to their cart and see if Sunday delivery is available in their region. Amazon Prime members can order as late as Friday and receive their packages on Sunday for free.

Until now, Amazon had only confirmed Sunday delivery in 17 markets, including New York and Los Angeles, where it first launched.

The other confirmed cities are Austin, Texas; Cincinnati, Ohio; College Station, Texas; Columbus, Ohio; Dallas, Texas; Houston, Texas; Indianapolis, Ind.; Lexington, Ky.; Louisville, Ky.; New Orleans, La.; Oklahoma City, Okla.; Philadelphia, Pa.; San Antonio, Texas; Shreveport, La.; and Waco, Texas.

But based on what we’re hearing and seeing, you can bet that Sunday delivery will be coming soon to a city near you.