Question: How many cadets nationwide are enrolled in the Army Reserve Officers' Training Corps, which one brigade is based out of Great Lakes Naval Training Center in Illinois?

Context paragraphs:
3rd Reserve Officers' Training Corps Brigade: The 3rd Reserve Officers' Training Corps Brigade is an Army Reserve Officers' Training Corps brigade based at the Great Lakes Naval Training Center, Illinois.

Army Reserve Officers' Training Corps: The Army Reserve Officers' Training Corps (ROTC, AROTC, or SROTC) is the United States Army component of the Reserve Officers' Training Corps.  It is the largest ROTC program, with 20,000 ROTC cadets in 273 ROTC programs at major universities throughout the United States.  These schools are categoriezed as Military Colleges (MC), Military Junior Colleges (MJC) and Civilian Colleges (CC).

Camp Allen: Camp Allen, is a small United States Marine Corps base in Norfolk, Virginia, a satellite of the Naval Station Norfolk.  In 1942 the Chief of the Bureau of Yards and Docks wanted the first Seabee training center close to an existing Naval training facility with Norfolk being chosen because of the available land that could be purchased.  On 25 March 1942 the Commandant of the 5th Naval District announced that the U.S. Naval Construction Training Center, Naval Operating Base Norfolk had been commissioned 4 days prior.  The base was named Camp Allen in memory of the CEC Captain Walter H. Allen founder of the naval construction regiment at Great Lakes Naval Training Center during WWI.  It is now home to both the 1st and 3rd Fleet Antiterrorism Security Team (FAST) Companies.  The base also houses a supply warehouse, battalion aid station, and a motor transport unit.  All units are members of the Marine Corps Security Force Regiment, headquartered aboard Naval Weapons Station Yorktown.

7th Reserve Officers' Training Corps Brigade: The 7th Reserve Officers' Training Corps Brigade is an Army Reserve Officers' Training Corps brigade based in Fort Knox, Kentucky.  It provides training support and oversight to all Army ROTC and Junior ROTC units in the states of Ohio, Indiana, Kentucky, Michigan, and Tennessee.

Northwoods battalion: The Northwoods Battalion is an Army Reserve Officers' Training Corps battalion that was established in 1968 at the University of Wisconsin-Stevens Point.  The battalion is a part of the 3rd Reserve Officers' Training Corps Brigade, the headquarters of which is based at the Great Lakes Naval Training Center, Illinois.

2nd Reserve Officers' Training Corps Brigade: The 2nd Reserve Officers' Training Corps Brigade is an Army Reserve Officers' Training Corps brigade based at Fort Dix, New Jersey.

8th Reserve Officers' Training Corps Brigade: The 8th Reserve Officers' Training Corps Brigade is a United States Army Reserve Officers' Training Corps brigade based at Joint Base Lewis-McChord, Washington.

4th Reserve Officers' Training Corps Brigade: The 4th Reserve Officers' Training Corps Brigade is a United States Army Reserve Officers' Training Corps brigade based in Fort Bragg, North Carolina.

1st Reserve Officers' Training Corps Brigade: The 1st Reserve Officers' Training Corps Brigade is an Army Reserve Officers' Training Corps brigade based at the Fort Knox, Kentucky.  This brigade is in charge of all military colleges and LTC.

6th Reserve Officers' Training Corps Brigade: The 6th Reserve Officers' Training Corps Brigade is an Army Reserve Officers' Training Corps brigade based at Hunter Army Airfield, Georgia.  It provides training support and oversight to all Army ROTC and Junior ROTC units in the states of Alabama, Georgia, Florida, Louisiana, Mississippi, and Puerto Rico.

Supporting paragraphs: 3rd Reserve Officers' Training Corps Brigade Army Reserve Officers' Training Corps
Answer: 20,000