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1099 Contractor in Colorado with a Illinois Client: Where Do You File?

Home state, plus the client state if you work thereNo withholding — 1099

Answer

Colorado always, Illinois sometimes. With no withholding on a 1099 the whole tax is yours to manage: estimate to Colorado through the year, and file a Illinois nonresident return for any income from work you physically performed in Illinois, claiming the credit back on the Colorado return.

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

  1. 1Quarterly estimated payments · Colorado

    Make quarterly estimated payments to Colorado Department of Revenue — Taxation Division on your full self-employment income — nothing is withheld from a 1099.

  2. 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.

  3. 3Resident return · ColoradoForm DR 0104CR

    File the Colorado resident return last and claim the credit for any tax paid to Illinois.

The two states, side by side

 ColoradoIllinois
Taxes wagesYes — flatYes — flat
Reciprocity partnersNone4 (Form IL-W-5-NR)
Convenience ruleNoNo
Nonresident returnForm DR 0104 with Schedule DR 0104PNForm IL-1040 with Schedule NR
Credit for other-state taxForm DR 0104CRSchedule CR
Nonresident safe harbourNone published30 days
Local income taxYesNo
Revenue departmentColorado Department of Revenue — Taxation DivisionIllinois Department of Revenue
Last verified

The other direction

Reversing the commute does not always reverse the answer. Living in Illinois and working in Colorado gives:Home state, plus the client state if you work there.

Illinois to Colorado →

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.

Other Colorado pairs

Questions people actually ask

I live in Colorado and my client is in Illinois. Do I have to file a Illinois tax return?

Colorado always, Illinois sometimes. With no withholding on a 1099 the whole tax is yours to manage: estimate to Colorado through the year, and file a Illinois nonresident return for any income from work you physically performed in Illinois, claiming the credit back on the Colorado return.

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 Colorado and Illinois hold an agreement makes no difference to a self-employed filer — sourcing rules decide the answer instead.

How current is this?

The Colorado and Illinois rules on this page were last checked against Colorado Department of Revenue — Taxation Division 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.