This is the orbat of the US Army as of late 1866:
The Army Reorganisation Act, 1866, set peace establishment strength at 54,302 officers and men, organised as:
45x 10 company infantry regiments (38th-41st to be colored and 42nd-45th to be invalids or "veteran reserves))
10x 12 company cavalry regiments (9th and 10th to be coloured)
5x 12 company artillery regiments, each fielding 2 batteries and a 10 company infantry battalion
1,000 Indian Scouts
The act was meant to consolidate the remaining volunteers into the regulars, with officers coming mainly from the volunteers. Ex-confederates were barred from service completely.
It also allowed for expansion to a war establishment of 75,382, although actual strength peaked in September '66 at 38,545.
Organisation was approximately (in early 1867):
General US Grant, commanding
LG WT Sherman, commanding the Military Division of the Missouri (Depts of Arkansas, the Missouri, the Platte, and Dakota)
MG Henry Halleck, commanding the Military Division of the Pacific (Depts of California and the Columbia)
Dept of the East
MG George Meade
1st Artillery (as infantry)
3rd Artillery (as infantry)
composite battalion of 4th Artillery (3 coys) and 40th Coloured Infantry (7 coys)
42nd Veteran Reserve Infantry
Dept of the Lakes
BG Joseph Hooker
Light Battery of 4th Artillery
3 coys, 4th Infantry
42nd Veteran Reserve Infantry
Dept of Washington
BG ERS Canby
3 coys, 5th Cavalry
7 coys, 4th Artillery (as infantry)
12th Infantry
30th Infantry
40th Colored Infantry
44th Veteran Reserve Infantry
Dept of the Potomac (Richmond, Va)
BG John Schofield
1 coy, 5th Cavalry
light battery of 5th Artillery
4 coys, 5th Artillery (as infantry)
11th Infantry
20th Infantry
21st Infantry
29th Infantry
Dept of the South
MG Dan Sickles
4 coys, 5th Cavalry
light battery of 3rd Artillery
6th Infantry
8th Infantry
Dept of the Tennessee
MG George Thomas
4 coys, 5th Cavalry
2nd Infantry
15th Infantry
16th Infantry
24th Infantry
25th Infantry
33rd Infantry
34th Infantry
45th Veteran Reserve Infantry
Dept of the Gulf
MG Philip Sheridan
4th Cavalry
6th Cavalry
9th Colored Cavalry
2 light batteries of 1st Artillery
6 coys, 5th Artillery (as infantry)
1st Infantry
7th Infantry
17th Infantry
26th Infantry
35th Infantry
39th Colored Infantry
41st Colored Infantry
Dept of the Arkansas
BG EOC Ord
light battery of 5th Artillery
19th Infantry
28th Infantry
37th Infantry
Dept of the Missouri
MG Winfield Hancock
2 coys, 2nd Cavalry
3rd Cavalry
7th Cavalry
9th Colored Cavalry
light battery of 4th Artillery
3rd Infantry
5th Infantry
38th Colored Infantry
Dept of the Platte (Iowa, Nebraska, Utah and some of Dakota Terr.)
BG Philip St. Geo. Cooke
10 coys, 2nd Cavalry
light battery of 3rd Artillery
13th Infantry
18th Infantry
27th Infantry
36th Infantry
Dept of Dakota (Minnesota, Montana Terr. and some of Dakota Terr.)
BG AH Terry
10th Infantry
22nd Infantry
31st Infantry
Dept of California
BG Irvin McDowell
8 coys, 1st Cavalry
8th Cavalry
2 light batteries of 2nd Artillery
6 coys of 2nd Artillery (as infantry)
9th Infantry
14th Infantry
32nd Infantry
Dept of the Columbia (Oregon, Washington Terr. and Idaho Terr.)
MG Frederick Steele
4 coys, 1st Cavalry
4 coys, 2nd Artillery (as infantry)
23rd Infantry
Two regular BGs were are without a command above, Rosecrans and Pope. Rosecrans would resign his Commission to become US Minister to Mexico (only to be fired by Grant as soon as he became President) and Pope has recently been relieved of of Dept of the Missouri, and will from April-Dec. '67 can assigned to the Dept of the Tennessee with disasterous results.