The strength of Grant's Army is interesting.
The Army of the Potomac used a different reporting system than the others, having moved special duty etc. men out of the PFD column. Other units did not do this. Hence the strength on 30th April was:
Army of the Potomac: 121,964 PFD on 30th April
9th Corps: 19,250 PFD on 30th April
= 141,214 PFD (vs 66,140, but rebel PFD is reckoned differently by not including slaves with the army)
As for reinforcements, on 30th April the District of SE Virginia, i.e. the forces Grant would absorb ca. Cold Harbor and the attempt at Petersburg, numbered 45,007 on the
30th April 1864 return.
On 15th June, Halleck write he's sent 55,178 reinforcements to Grant, and
listed them by regiment. This includes a recent draft of 5,000. The
depots reported more than 34,645* at Belle Plain or Port Royal and 12,181 arriving at White House prior to the 10th June. Thus Halleck's figure is reasonable.
* a veteran battalion, 6 batteries and a cavalry detachment are not enumerated.
This excludes direct recruiting recruits, of which Humphreys says only 2,453 were received.
Reinforcements:
From Washington: 55,178
From SE Va: 45,007
By Recruiting: 2,453
= 102,683
Total troops available (in PFD): 243,852
There is a claim that 36-7 regiments were due to muster out, and left by 12th June. This comes from Humphreys, but is repeated by Rhea. Only regiments enlisted for three years right at the beginning of the war were due for muster out (indeed, one regiment that did was the 1st Massachusetts, the "First Defenders of Washington").
I could only find six regiments that mustered out, and the two brigades of Pennsylvania Reserves with the army consolidated into two regiments. The total loss to the army was less than 2,000 men.
If anyone can find regiments that mustered out, please let me known.