725 ILCS 220/4

(725 ILCS 220/4) (from Ch. 38, par. 156-4)

Sec. 4.

Exemption
from arrest and service of process.

If a person comes into this state in obedience to a summons directing
him to attend and testify in this state he shall not, while in this state
pursuant to such summons be subject to arrest or the service of process,
civil or criminal, in connection with matters which arose before his
entrance into this state under the summons.

If a person passes through this state while going to another state in
obedience to a summons to attend and testify in that state or while
returning therefrom, he shall not while so passing through this state be
subject to arrest or the service of process, civil or criminal, in
connection with matters which arose before his entrance into this state
under the summons.

(Source: Laws 1959, p. 2147.)