Is the US Army Rangers a division?

No. It is a Regiment. The 75th Ranger Regiment has three line battalions, a special troops battalion that handles training/selection for new Rangers, a new Military Intelligence battalion is being stood up, according to Army Times, and I reckon there's an HQ battalion, but don't be surprised to hear Rangers talk like there are only three battalions.

Mr. Boyd, the 75th Rangers known today are a Regiment. They were once divided into battalions prior to 1986, into the 75th Ranger Infantry LRRS companies in Vietnam, 15 companies during Korea, then Battalions during WWII.

In 1969-1970 each division and separate Brigade had a Long Range Surveillance unit (a numbered detachment or company and a handful of lettered companies in multiple Infantry Battalions, some were provisional, meaning they stood them up out of Hide) referred to as LRRPs. They were converted to lettered Ranger Companies. My uncle served in 4 ID's Ranger company. A book about this is Charlie Rangers, one of the authors is Rotondo. Another series of books on it is Six Men Silent by Rey Martinez. Fiction books Charlie Mike and The Last Run are about a Vietnam era Ranger Company, author is Leonard B Scott LTC(R).....So no, the Army Rangers is NOT a Division. Currently they are a Regiment. Ranger qualified soldiers serve through out the Army. Not all Rangers are in the 75th.

In the 1970s they were all deactivated. The 75th Ranger Regiment and subordinate battalions were activated. An Army Regiment is an equivalent sized organization to a Brigade or Group commanded by a Colonel. Regiments only really exist as a unit in the 75th Ranger Regiment and active Army Cavalry Regiments (2d, 3D, 11th). There are regiments for Heraldry purposes and they are roughly affiliated with BCTs, but it is not homogenous. 4BCT, 101ABN (Currahee) was affiliated with the 506th PIR, however their RSTA Squadron was affiliated with 61st Cavalry Regiment as were several other RSTA Squadrons even in other divisions (Clint Romesha and Ty Carter were in another Squadron affiliated with 61st). Our FA Battalion was affiliated with 320th FA (Guns of Glory) which traces its routes back to the 82d ABN. The FA BNs across the 101st were all Battalions in the 320th. Similarly 4BCT, 82d ABN (TF Fury) was affiliated with 508th PIR. 2BCT 101st (Strike) is affiliated with 502 PIR. 1BCT, 101st (Bastogne) is affiliated with 327 IN. 187th IN Regiment is affiliated with 3BCT 101st (Rakkasans).

The last time the Army really fought as Regiments was Korea. Then the Army formed Battle Groups in the Pentomic structure, which was DOA. Then the Army formed Brigades and spread the Battalions and their Regimental affiliations around the Army. The Combat Arms Regimental System was born, trying to capitalize on the pride and esprit de corps of the British Regimental system. The original idea was that a soldier would PCS unit to unit, but in different Battalions in That same Regiment, yeah didn't turn out. Soldiers now wear their Regimental affiliation over their nameplate. It could be branch designated like Ordnance Corps for Ordnance soldiers and officers. It could be a combat arms Regiment for Infantry, Armor, FA, etc which is either their first unit or recently, a unit they successfully served in IAW AR 670-1.