What is now referred to as the "classic Chicago style" was developed in the late 1940s and early 1950s, taking Delta blues, amplifying it and putting it into a small-band context. Adding drums, bass, and piano (sometimes saxophones) to the basic string band and harmonica aggregation, the genre created the now standard blues band lineup. The form was (and is) flexible to accommodate singers, guitarists, pianists and harmonica players as the featured performer in front of the standard instrumentation. Later permutations of the style took place in the late 1950s and early 60s with new blood taking their cue from the lead guitar work of B.B.King and T-Bone Walker, creating the popular West Side sub genre which usually featured a horn section appended to the basic rhythm section. Although the form embraced rock beats and modern funk rhythms in the '80s and '90s, it has since generally stayed within the guidelines developed in the 1950s and early 60s.

Quote from Cub Koda at All-Media Guide.

Chicago Blues are hard-edged and loud because Chicago is a hard-edged, tough industrial city in which you have to be more powerful and louder in order to be heard.

Some well-known musicians who play or have played the Chicago Blues are B.B. King, Junior Wells, Howlin' Wolf, and Muddy Waters.

Quote from Knowledge Adventure.

CHICAGO is the blues capitol of the world — a musical metropolis filled with the electrified sounds of snarling guitars, howlin' vocals, and big city rhythms. Striking a chord with Chicago audiences in the 1930's, the Chicago blues sound has continued to hold listeners firmly by the ears to this very day.

Quote from A Chicago Blues Tour at Big Chicago Record