The 16.2 inches recorded at O'Hare just during the hours of February 1st (out of 19.3 inches total) were the most ever for any February day in Chicago.  The 10.5 inches recorded on February 1st at Rockford (out of 11.9 inches total) ranked #2 all time for the date and #3 all time for any February day in Rockford.  For the event as a whole, the 19.3 inches at O'Hare ranks as #5 out of all snow events in Chicago, while the 11.9 inches at Rockford ranks as #10 overall for that city.
Several ingredients came together to produce this significant snowfall total.  A deepening center of low pressure lifting from the Southern Plains through the Ohio Valley pulled rich moisture out of the tropical Pacific Ocean and the Gulf of Mexico and wrapped it into cold Arctic air.  Early in the event the relatively mild surface temperatures in the 30s kept snow-to-liquid ratios on the lower end of the spectrum, or close to 10-to-1.  As the event progressed and colder air spread into the region, the snow evolved from wet and heavy to very light and fluffy as ratios eventually increased to 30-to-1 or higher.  At O'Hare the liquid precipitation total of 0.87 on Sunday was a record for February 1st, exceeding the previous record of 0.77 measured during the Groundhog Day Blizzard of 2011.
A tightening pressure gradient around the low center as it moved from central Illinois into central Indiana also supported strong and gusty northeast winds later Sunday afternoon into the evening, producing a period of blizzard to near blizzard conditions with gusts over 35 mph and visibilities around 1/4 mile or less in many locations.
Some of the highest storm total snow reports include:  22.0 inches near Lincolnshire (Lake); 21.5 inches in Oak Lawn (Cook); 20.8 inches in Elmhurst (DuPage); 18.0 inches near Harvard (McHenry); 17.5 inches near Marseilles (La Salle); 16.8 inches west of Plainfield (Kendall); 16.8 inches in Batavia (Kane); 16.5 inches near Lockport (Will); 15.9 inches in DeKalb (DeKalb); 15.3 inches in Paw Paw (Lee); 15.2 inches in Morris (Grundy); 14.5 inches near Bourbonnais (Kankakee); 14.4 inches near Rockford (Winnebago); 14.0 inches in Rochelle (Ogle); 12.0 inches in Belvidere (Boone); 7.6 inches near Ashkum (Iroquois); 7.0 inches in Paxton (Ford); and 6.5 inches in Dwight (Livingston).
Some of the strongest wind measurements include: 52 mph near Waukegan; 49 mph near Shorewood; 44 mph at Rockford Airport; 44 mph at DuPage Airport; 43 mph at Aurora Airport; 43 mph at Paxton; and 40 mph near La Salle.

Blizzard in WINNEBAGO, ILLINOIS
From 01-FEB-15 00:00:00 to 02-FEB-15 04:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Winnebago ESDA reported white out conditions across the county with many vehicles stranded.

Blizzard in BOONE, ILLINOIS
From 01-FEB-15 00:00:00 to 02-FEB-15 04:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Boone County sheriff reported white out conditions across the county with many rural roads closed.

Blizzard in LEE, ILLINOIS
From 01-FEB-15 00:00:00 to 02-FEB-15 04:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Lee County EM reported white out conditions across the county with many roads closed. State Route 52  was closed south of Dixon near the I-88 interchange due to stranded cars.

Blizzard in OGLE, ILLINOIS
From 01-FEB-15 00:00:00 to 02-FEB-15 04:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Whiteout conditions were reported along with numerous stranded vehicles.  Highway 52 was down to one lane due to severe drifting.

Blizzard in DE KALB, ILLINOIS
From 01-FEB-15 00:00:00 to 02-FEB-15 04:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

De Kalb County had to pull their plow fleet from the roads around 6 pm after the snow ended due to dangerous conditions.

Heavy Snow in MCHENRY, ILLINOIS
From 01-FEB-15 00:00:00 to 02-FEB-15 04:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

There were a few stranded vehicles along with some drifting along and temporary whiteout conditions.

Blizzard in LAKE, ILLINOIS
From 01-FEB-15 00:00:00 to 02-FEB-15 08:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Blizzard in KANE, ILLINOIS
From 01-FEB-15 00:00:00 to 02-FEB-15 04:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

ILDOT reported Route 52 was closed due to blowing and drifting snow. Whiteout visibility was reported.

Heavy Snow in DU PAGE, ILLINOIS
From 01-FEB-15 00:00:00 to 02-FEB-15 08:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy Snow in COOK, ILLINOIS
From 01-FEB-15 00:00:00 to 02-FEB-15 08:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Official NWS Observations

Heavy Snow in KANKAKEE, ILLINOIS
From 01-FEB-15 00:00:00 to 02-FEB-15 04:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy Snow in FORD, ILLINOIS
From 01-FEB-15 00:00:00 to 02-FEB-15 04:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy Snow in IROQUOIS, ILLINOIS
From 01-FEB-15 00:00:00 to 02-FEB-15 04:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy Snow in KENDALL, ILLINOIS
From 01-FEB-15 00:00:00 to 02-FEB-15 04:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy Snow in GRUNDY, ILLINOIS
From 01-FEB-15 00:00:00 to 02-FEB-15 04:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

ILDOT reported numerous accidents and particularly bad blowing and drifting of snow on I-80 near on the western side of the county.

Heavy Snow in WILL, ILLINOIS
From 01-FEB-15 00:00:00 to 02-FEB-15 08:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Emergency managers reported blowing and drifting in open areas along with stranded vehicles.  Temporary whiteout conditions were reported on sections of I-80 and I-55.

Heavy Snow in LA SALLE, ILLINOIS
From 01-FEB-15 00:00:00 to 02-FEB-15 04:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Emergency managers reported U.S. 34 was closed between Mendota and Earlville due to blowing snow and stranded vehicles.  Route 18 between U.S. 251 and Streator was also closed.

Heavy Snow in LIVINGSTON, ILLINOIS
From 01-FEB-15 00:00:00 to 02-FEB-15 04:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter