How many troops did each army of the civil war have in each year of the war from 1861-1864 and how many casualties did they have each year?
As I remember, at the beginning of 1861 there were about 16,000 soldiers in the United States Army, the regular army, and the United States Volunteers were not yet formed.
And at the beginning of 1861 the Confederate States of American was not yet formed and didn't have any armed forces.
By January 1865 the Confederate army had already some time earlier reached its maximum size and had been declining rapidly in numbers for some time, probably having about 200,000 to 300,000 total men available for duty in January 1865.
The total number of Union soldiers reached about 1,000,000 in May 1865, when enlistment stopped and men started to be discharged. At that time there were about 600,000 men available for duty out of the 1,000,000 enlisted.
I remember seeing a table somewhere like you asked about, with the numbers of Union and Rebel soldiers for each year of the war, but I have not found it yet.
Here is something:
In July 1861, the two armies were nearly equal in strength with less than 200,000 soldiers on each side; however at the peak of troop strength in 1863, Union soldiers outnumbered Confederate soldiers by a ratio of 2 to 1. The size of Union forces in January 1863 totaled over 600,000. Two years later, that number had not changed dramatically for the Union Army but had dropped to about 200,000 for the Confederate Army.
Here is a link to a chart with the size of the United States armed forces by branch each year from 1789 to 1997: