1099 Contractor in Illinois with a Connecticut Client: Where Do You File?
Answer
Pay Illinois by instalments, and watch your Connecticut days. Reciprocity agreements do not help here: every one of them covers wage withholding, and a 1099 has no withholding to switch off. Illinois taxes the full profit, Connecticut taxes the on-site share, and the Illinois credit reconciles them.
Last verified
The client's location is the wrong thing to track. What matters is where you were sitting when you did the work — which is why a contractor's exposure to Connecticut is measured in days on the ground rather than in invoices sent.
Connecticut publishes no de minimis day count or dollar floor for nonresidents. Any Connecticut-source wage income above the state's general filing threshold requires a nonresident return, and that threshold is reset each year — check the current figure on the Connecticut Department of Revenue Services nonresident instructions before filing.
What you file
- 1Quarterly estimated payments · Illinois
Make quarterly estimated payments to Illinois Department of Revenue on your full self-employment income — nothing is withheld from a 1099.
- 2Nonresident return · ConnecticutForm CT-1040NR/PY
File a Connecticut nonresident return only if you performed services inside Connecticut. Connecticut publishes no de minimis day count or dollar floor for nonresidents. Any Connecticut-source wage income above the state's general filing threshold requires a nonresident return, and that threshold is reset each year — check the current figure on the Connecticut Department of Revenue Services nonresident instructions before filing.
- 3Resident return · IllinoisSchedule CR
File the Illinois resident return last and claim the credit for any tax paid to Connecticut.
The two states, side by side
| Illinois | Connecticut | |
|---|---|---|
| Taxes wages | Yes — flat | Yes — graduated |
| Reciprocity partners | 4 (Form IL-W-5-NR) | None |
| Convenience rule | No | Only against convenience-rule states |
| Nonresident return | Form IL-1040 with Schedule NR | Form CT-1040NR/PY |
| Credit for other-state tax | Schedule CR | Schedule 2 (Form CT-1040) |
| Nonresident safe harbour | 30 days | None published |
| Local income tax | No | No |
| Revenue department | Illinois Department of Revenue | Connecticut Department of Revenue Services |
| Last verified |
The other direction
Reversing the commute does not always reverse the answer. Living in Connecticut and working in Illinois gives:Home state, plus the client state if you work there.
Same two states, different situation
The withholding answer turns on how you are paid and where the work happens, not only on which two states are involved.
- W-2 commuter: Illinois → ConnecticutBoth states — credit offsets the double tax
- Remote worker: Illinois → ConnecticutHome state only
- Moved mid-year: Illinois → ConnecticutTwo part-year returns
Other Illinois pairs
Questions people actually ask
I live in Illinois and my client is in Connecticut. Do I have to file a Connecticut tax return?
Pay Illinois by instalments, and watch your Connecticut days. Reciprocity agreements do not help here: every one of them covers wage withholding, and a 1099 has no withholding to switch off. Illinois taxes the full profit, Connecticut taxes the on-site share, and the Illinois credit reconciles them.
Do reciprocity agreements help a 1099 contractor?
No. Every state reciprocity agreement in the country is an arrangement about wage withholding between two revenue departments, and a 1099 has no withholding to switch off. Whether Illinois and Connecticut hold an agreement makes no difference to a self-employed filer — sourcing rules decide the answer instead.
How current is this?
The Illinois and Connecticut rules on this page were last checked against Illinois Department of Revenue and Connecticut Department of Revenue Services on 2026-08-07. We re-check the full grid every December after state legislative sessions close, and re-check the convenience-of-the-employer states quarterly because that is where the rules move fastest.
Sources
Every fact above comes from the revenue department that publishes the rule. We do not cite secondary summaries, and we do not restate a figure we could not find at source.
- Illinois Department of Revenue — individual income taxaccessed 2026-08-07
- Connecticut Department of Revenue Services — individual income taxaccessed 2026-08-07