Passport Agency Appointments (same day expedited service)
Appointments for same-day expedited service often go quickly. It is best that you schedule your appointment with the passport agency exactly 14 days before your trip. You will want to call the passport number before the center opens at 8am EST as they will have just opened up one day (14 days out) of appointments at all agencies. Appointment times start at 8am. It is important that you have enough buffer in your travel schedule. For example, if you make an appointment for a new passport at 11am and your time of travel is at 2pm, there will not be enough time for you to get your passport. If you book the 8am slot you may have to wait until the end of the business day to get your new passport or it may only be a few hours.

You will want to have your date of travel, time of travel, your flight itinerary number, name of destination, full name of applicant, and applicant's birth city, and the zip code of where you live (to help them find the closest available center with open slots). Use the following steps to increase your chances of success to booking an appointment as they can go very quickly:

1. 14 days before your trip, you need to schedule an appointment with the passport agency.
2. At 7:55 am call the passport number 877-487-2778 (This have to be exactly 14 days before your plane ticket or less. If less, it will get harder to find an appointment)
3. Click 1 (For English)
4. Click 1 (New Passport)
5. Continue to Click 7 to repeat, and keep doing this while watching your watch or using Time.gov to get the exact time down to the second.
6. When your it hits exactly 8:00 am Click 2 (for traveling within 14 days option)
7. There will be a delay of 3-4 second and you will wait for the next available agent. If you are very lucky, you will be put straight through to an agent. You may be waiting few minutes or maybe as long as 15-20 minutes.
8. If you did not click 1 exactly at 8 am, you may have to wait for more than an hour and half

After the appointment slot has been reserved you will be provided with a unique identifier code and reservation number. These details will also be emailed to you.

Credit: chgoeditor

Known office locator numbers (not complete)
Note: The office code (first two digits of your application locator number returned by Passport Status) is the office reviewing your documents and approving your application. It isn't necessarily the address you mailed the forms to (always Irving or Philadelphia for renewals) nor the facility where the book is physically printed and mailed (often Tucson or Hot Springs).

10: Boston
11: NYC
12: Honolulu
14: Stamford, CT
15: Portsmouth, NH
17: Aurora, CO
18: Chicago
19: Washington, DC
20-29: Portsmouth, NH
34: Charleston
40-42: New Orleans, LA
50: Los Angeles, CA
51: Miami
53: Seattle
54: Minneapolis
55: Dallas or Hot Springs, AR (?)
56: Detroit
57: San Francisco
58: Philadelphia, PA
61: Tucson
62: Tucson
67: San Juan, PR
68: Portsmouth, NH
69: Portsmouth, NH
71: US embassies/consulates abroad
74: Atlanta
75: St Albans, VT
76: San Diego, CA
77: Buffalo, NY
78: El Paso, TX
79: Houston, TX
95: Online

A list of agencies and their locator numbers is listed on this page under the heading, "List of passport agencies and centers with locator numbers."

H/T Nayef, txviking, and various individual posts both here and on Reddit. If you have a locator not in the above list, check the return address agency name or postmark/ZIP on your returned citizenship docs, or passport card if you applied for one, which may be the processing office, although the address itself is likely to be a PO Box in Sterling, VA in all cases (which appears to be a lockbox location that processes mail for all locations). The passport books are printed in fewer locations, often Hot Springs and Tucson, and may not correspond to the agency where the processing steps occurred. If it doesn’t match the list above, please add or correct.