The short answer
A defendant can bring in others who may share responsibility, through a third-party complaint against a new party or a counterclaim against a co-defendant. Illinois lets defendants who share liability seek contribution based on relative fault.
Where it fits in your case
Usually with or soon after the answer. Later filings need the court’s permission.
What to expect
Third-party complaints under 735 ILCS 5/2-406(b) can seek contribution, indemnity, or contract damages.
Contribution timing. When the main case is pending, a contribution claim generally must be brought in that case.
Good-faith settlements can cut off other defendants’ contribution claims against the settling party.
Fault under 25 percent can limit a defendant to several liability for some damages (735 ILCS 5/2-1117).
What we need from you
Subcontracts, vendor agreements, certificates of insurance, and anything showing who else was involved.
Common misconceptions
“We can sort out contribution after the case.” That claim may be barred by then.
“More defendants always helps.” It also adds cost and delay.