It was named after Conrad Will, a politician and businessman involved in salt production in southern Illinois.

"WILL, a county in the E. N. E. part of Illinois, bordering on Indiana, has an area of 1,236 square miles (3,200 km2).

It is intersected by the Kankakee and Des Plaines Rivers, branches of the Illinois.

The surface is generally level, and destitute of timber, excepting small groves.

The soil of the prairies is a deep, sandy loam, adapted to Indian corn and grass.

In 1850 the county produced 527,903 bushels of Indian corn; 230,885 of wheat; 334,360 of oats; 32,043 tons of hay, and 319,054 pounds of butter.

Named in honor of Conrad Will, for many years a member of the Illinois legislature.

The 17,000 acres (69 km2) Midewin National Tallgrass Prairie is a U.S. Forest Service park in the county on the grounds of the former Joliet Arsenal.

[15] In terms of ancestry, 21.6% were German, 18.6% were Irish, 13.3% were Polish, 11.1% were Italian, 5.9% were English, and 2.1% were American.

[18] The fourth courthouse was designed of reinforced concrete in the Brutalist style by Otto Stark of C.F.

Citing lack of space, inefficiency and high operating costs, the County Board chose to erect a new courthouse, which was designed by Wight & Co. and completed in 2020.

[20] After a number of votes and appeals, demolition was approved and the destruction of the building began on December 4, 2023.

It voted for the national winner in every presidential election from 1980 to 2012, but Chicago-born Hillary Clinton won it along with the rest of the "collar counties" aside from McHenry in 2016.

Four different Metra commuter rail lines (Metra Electric Main Line, Southwest Service, Rock Island District and Heritage Corridor) connect Will County with the Chicago Loop.