605 ILCS 5/6-118
Every person elected or appointed to the office of highway commissioner, and to consolidated township road district clerk in counties under township organization and to district clerk in counties not under township organization, before he enters upon the duties of his office, and within 10 days after he is notified of his election or appointment, shall take and subscribe, before some judicial officer of the circuit court or district or town clerk, the oath or affirmation of office prescribed by the Constitution, which oath or affirmation shall, within 5 days thereafter, be filed with the district or town clerk.
In counties under township organization no additional oath shall be required of the town clerk to enable him to enter upon the discharge of the duties of his office as ex-officio clerk for the highway commissioner.
If any person elected or appointed to either of the offices above named neglects to take and subscribe such oath, and cause the same to be filed as above required, such neglect shall be deemed a refusal to serve.
605 ILCS 5/6-118