Here's something many Australian owners of US S corporations don't realize: Form 1120-S is a US federal return tied to the corporation, not the shareholder. Living in Sydney or Melbourne doesn't change the filing obligation if you hold shares in a US S corp.
This guide walks through who must file, how to pinpoint the right IRS filing center, when e-filing makes more sense than paper, and the mistakes that cause returns to bounce back or get delayed.
Key Takeaways
- S corporations file Form 1120-S annually; shareholders report their share on Schedule K-1.
- Paper-filing addresses depend on business location, assets, and Schedule M-3 status, not shareholder residence.
- Pull mailing addresses from current IRS sources, not older third-party lists.
- E-filing removes the address question, though eligibility rules and mandatory thresholds still apply.
What Form 1120-S Is and Who Needs to File It
Form 1120-S is the annual U.S. federal income tax return S corporations use to report income, deductions, gains, losses, credits, and shareholder allocations for the tax year.
Who's required to file:
- Any U.S. domestic corporation with an accepted and effective S election
- An LLC that made a valid election to be taxed as an S corporation
- Entities with little or no business activity during the year, as long as the election remains in effect
There's no inactivity exemption built into this rule. An S corporation with zero revenue still files, because the obligation is tied to the election status, not to whether money moved.
Form 1120-S vs. Schedule K-1 vs. Form 1120
Form 1120-S belongs to the corporation. Schedule K-1 belongs to each shareholder — it reports their individual share of income, deductions, and credits, which then flows onto their personal return. A shareholder can owe tax on their K-1 share even if the corporation never distributed cash.
Don't confuse this with Form 1120, the standard return for C corporations. The two forms serve different entity types, carry different tax treatments, and are mailed to different addresses in many cases. Filing the wrong one, or mailing it to the wrong centre, creates processing headaches that take months to untangle.
Before assuming your filing obligations, check the current-year IRS instructions. Eligibility rules, required schedules, and special filing situations can shift from one tax year to the next.
How to Determine Where to File Form 1120-S
Forget the shareholder's home address or the accountant's office. The IRS routes paper returns based on the corporation's principal business, office, or agency location: that is the anchor point for everything that follows.
Two other factors modify the address:
- Total year-end assets: whether the corporation is above or below the $10 million threshold
- Schedule M-3 status: whether the return includes this schedule, regardless of asset size
Domestic Filing Address Table
| Principal location | Assets / Schedule M-3 | Mailing address |
|---|---|---|
| Group A states* | Under $10M AND no Schedule M-3 | Department of the Treasury, Internal Revenue Service, Kansas City, MO 64999-0013 |
| Group A states* | $10M or more OR Schedule M-3 filed | Department of the Treasury, Internal Revenue Service, Ogden, UT 84201-0013 |
| Group B states** | Any amount | Department of the Treasury, Internal Revenue Service, Ogden, UT 84201-0013 |
| Foreign country or US possession | Any amount | Internal Revenue Service, P.O. Box 409101, Ogden, UT 84409 |
*Group A: Connecticut, Delaware, DC, Georgia, Illinois, Indiana, Kentucky, Maine, Maryland, Massachusetts, Michigan, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Vermont, Virginia, West Virginia, Wisconsin.
**Group B: Alabama, Alaska, Arizona, Arkansas, California, Colorado, Florida, Hawaii, Idaho, Iowa, Kansas, Louisiana, Minnesota, Mississippi, Missouri, Montana, Nebraska, Nevada, New Mexico, North Dakota, Oklahoma, Oregon, South Dakota, Texas, Utah, Washington, Wyoming.
Attaching Schedule M-3 redirects a Group A filer to Ogden even when assets sit below the $10 million line. That's an easy detail to miss if you're working from memory rather than the current IRS where-to-file page.
Filing From Australia or Another Foreign Country
If the S corporation's principal office sits outside the US, use the Ogden P.O. Box 409101 address above. But note: having an Australian-based owner doesn't itself trigger this row. What matters is where the corporation conducts business and maintains its principal office.
The IRS requires S corporations to be domestic entities and generally prohibits nonresident-alien shareholders. An overseas owner's address is not what determines routing: the corporation's own business location is.
Before you mail, confirm:
- Correct tax year on the form
- Principal business location
- Total year-end assets
- Schedule M-3 requirement
- Payment status (paid separately or not)
- Whether your chosen address works for USPS, private carrier, or both
Older blog posts and PDFs circulate outdated addresses constantly. Always cross-check against the IRS's current published table before sealing the envelope.
How to Mail Form 1120-S Correctly
Paper filing follows a specific sequence, and skipping steps is how returns get rejected or delayed.
- Complete Form 1120-S in full, leaving no required fields blank
- Prepare all applicable schedules and attachments, labelled with the corporation's name and EIN
- Generate a Schedule K-1 for every shareholder, attached after page 5 in the IRS's prescribed order
- Sign and date the return: an authorized officer (president, vice president, treasurer, assistant treasurer, or chief accounting officer) must sign
- Retain a complete copy before mailing, including proof of what was sent
Mailing vs. Private Delivery Services
USPS and private couriers aren't interchangeable at the address level. IRS P.O. Box addresses only accept USPS delivery. If you're using a private carrier, you need the matching street address instead:
| Assigned center | Street address for private delivery |
|---|---|
| Kansas City | 333 W. Pershing, Kansas City, MO 64108 |
| Ogden | 1973 Rulon White Blvd., Ogden, UT 84201 |
Only designated services from approved carriers (DHL Express, FedEx, UPS: specific service tiers, not just the brand name) qualify for the IRS's timely-mailing-as-timely-filing rule, according to the IRS's delivery service list. Keep written proof of the mailing date from whichever carrier you use.
Practical safeguards:
- Use a trackable mailing service every time
- Keep both the mailing receipt and delivery confirmation
- Double-check all K-1s and required schedules are attached before sealing
- Hold onto evidence of timely mailing for at least several years
Payment itself typically isn't mailed with a paper check anymore. The IRS directs balance-due payments and estimated tax installments through electronic channels like EFTPS or a business tax account.
Common mistakes that trip up filers:
- Using the Form 1120 address instead of the 1120-S address
- Omitting K-1s or required schedules entirely
- Sending a P.O. Box address through a private carrier that can't deliver there
- Leaving required fields blank and writing "see attached" instead
- Copying an address from an outdated source
For S corporations juggling foreign shareholders, multi-country bookkeeping reconciliations, or dense 1120-S schedules, getting outside support from VJM Global's accounting and tax compliance team can prevent exactly these kinds of errors before they reach the mailbox.
Can Form 1120-S Be E-Filed? Deadlines and Extensions
Yes: most S corporations can e-file through approved tax software or a qualified tax professional acting as an authorized IRS e-file provider. E-filing sidesteps the whole address question, since there's no physical destination to choose.
E-Filing vs. Paper Filing
| Factor | E-file | Paper file |
|---|---|---|
| Address selection | Not applicable | Required, based on location/assets/M-3 |
| Delivery proof | IRS acknowledgment | Mailing receipt/carrier confirmation |
| Rejected returns | Corrected and resubmitted electronically | Requires remailing |
| Mandatory for some filers | Yes, above a threshold | N/A |
E-filing becomes mandatory once an S corporation files 10 or more returns of any type during the calendar year, counting income, employment, excise, and information returns together per the IRS instructions. That's an aggregate count across all return types, not a 1120-S-specific threshold. Hardship waivers and a religious exemption (noted at the top of page 1) are available in limited circumstances.
Deadlines, Extensions, and Penalties
The standard due date is the 15th day of the third month after the tax year ends. For a calendar-year 2025 return, that falls on March 16, 2026, since March 15 fell on a Sunday. When the due date hits a weekend or federal holiday, the deadline rolls to the next business day.
Need more time? Form 7004 grants a general six-month extension to file, but it doesn't extend your time to pay. Estimate and pay any tax owed by the original due date regardless of the extension.
A dissolved S corporation still has a final filing obligation, generally due by the 15th day of the third month after dissolution, with "final return" and "final K-1" boxes marked accordingly.
Late filing isn't cheap. For 2025 returns, the penalty runs $255 per month or partial month (up to 12 months), multiplied by the number of shareholders during the tax year, and that's before adding 5% of unpaid tax per month if a balance is due. For returns required in 2027, that monthly amount rises to $260 under inflation adjustments.
Frequently Asked Questions
Where do I file Form 1120-S?
It depends on your corporation's principal business location, total assets, and whether Schedule M-3 is attached. Check the current IRS Form 1120-S filing instructions before mailing, since addresses change over time.
Can Form 1120-S be filed electronically?
Yes, through approved tax software or a tax professional registered as an authorized e-file provider. Some corporations must e-file once they exceed the aggregate 10-return threshold.
What IRS form do S corporations file?
S corporations file Form 1120-S for the corporate-level federal income tax return. Shareholders then use their Schedule K-1 figures on their personal tax returns.
What's the difference between Form 1120 and Form 1120-S?
Form 1120 is the standard return for C corporations, while Form 1120-S is specifically for S corporations. They carry different tax treatments, reporting requirements, and in many cases different mailing addresses.
