1099 Contractor in Connecticut with a Illinois Client: Where Do You File?
Answer
Pay Connecticut by instalments, and watch your Illinois days. Reciprocity agreements do not help here: every one of them covers wage withholding, and a 1099 has no withholding to switch off. Connecticut taxes the full profit, Illinois taxes the on-site share, and the Connecticut 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 Illinois is measured in days on the ground rather than in invoices sent.
Illinois allows a 30-day safe harbour before the obligation attaches. Illinois does not require an employer to withhold from a nonresident who works in Illinois for 30 or fewer days in the year. The day count is a withholding safe harbour; a nonresident who exceeds it owes Illinois tax on the Illinois-source wages.
What you file
- 1Quarterly estimated payments · Connecticut
Make quarterly estimated payments to Connecticut Department of Revenue Services on your full self-employment income — nothing is withheld from a 1099.
- 2Nonresident return · IllinoisForm IL-1040 with Schedule NR
File a Illinois nonresident return only if you performed services inside Illinois. Illinois does not require an employer to withhold from a nonresident who works in Illinois for 30 or fewer days in the year. The day count is a withholding safe harbour; a nonresident who exceeds it owes Illinois tax on the Illinois-source wages.
- 3Resident return · ConnecticutSchedule 2 (Form CT-1040)
File the Connecticut resident return last and claim the credit for any tax paid to Illinois.
The two states, side by side
| Connecticut | Illinois | |
|---|---|---|
| Taxes wages | Yes — graduated | Yes — flat |
| Reciprocity partners | None | 4 (Form IL-W-5-NR) |
| Convenience rule | Only against convenience-rule states | No |
| Nonresident return | Form CT-1040NR/PY | Form IL-1040 with Schedule NR |
| Credit for other-state tax | Schedule 2 (Form CT-1040) | Schedule CR |
| Nonresident safe harbour | None published | 30 days |
| Local income tax | No | No |
| Revenue department | Connecticut Department of Revenue Services | Illinois Department of Revenue |
| Last verified |
The other direction
Reversing the commute does not always reverse the answer. Living in Illinois and working in Connecticut 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: Connecticut → IllinoisBoth states — credit offsets the double tax
- Remote worker: Connecticut → IllinoisHome state only
- Moved mid-year: Connecticut → IllinoisTwo part-year returns
Other Connecticut pairs
Questions people actually ask
I live in Connecticut and my client is in Illinois. Do I have to file a Illinois tax return?
Pay Connecticut by instalments, and watch your Illinois days. Reciprocity agreements do not help here: every one of them covers wage withholding, and a 1099 has no withholding to switch off. Connecticut taxes the full profit, Illinois taxes the on-site share, and the Connecticut 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 Connecticut and Illinois hold an agreement makes no difference to a self-employed filer — sourcing rules decide the answer instead.
How current is this?
The Connecticut and Illinois rules on this page were last checked against Connecticut Department of Revenue Services and Illinois Department of Revenue 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.
- Connecticut Department of Revenue Services — individual income taxaccessed 2026-08-07
- Illinois Department of Revenue — individual income taxaccessed 2026-08-07