A Partial List of Units Equipped With the Spencer During the Civil War

The following is a list of units, as best as I can ascertain, that were at least partially armed with Spencer rifles or carbines, the greatest majority of these being armed with carbines.

1st Michigan Cav.	*2nd Michigan Cav.	3rd Michigan Cav.	*4th Michigan Cav.
5th Michigan Cav.	6th Michigan Cav.	7th Michigan Cav.	1st New York Cav.
*1st Ohio Cav.	2nd Ohio Cav.	*3rd Ohio Cav.	*4th Ohio Cav.
5rd Ohio Cav.	7th Connecticut.	*8th Iowa.	*4th Kentucky Mounted Infantry.
*4th Indiana.	*6th Kentucky.	*1st Wisconsin.	*2nd Indiana.
*3rd Iowa.	*4th Iowa.	*10th Missouri.	*7th Kentucky.
*5th Iowa.	*7th Ohio Cav.	*7th Pa Cav.	*1st U.S Cav.
+*17th Indiana.	+*72nd Indiana.	+*92nd Illinois.	+*98th Illinois.
+*123rd Illinois.	57th Massachusetts.	37th Massachusetts.	1st New York.
5th Independent Company of Ohio Sharpshooters.	6th Independent Company of Ohio Sharpshooters.	7th Independent Company of Ohio Sharpshooters.	8th Independent Company of Ohio Sharpshooters.

^*Part of Wilson's raid on Selma
⁺Member of Wilder's Lightning Brigade

According to U.S. Army Ordinance records, 11471 rifles and  95,161 carbines were issued by War's end.

I'll be adding and correcting this list as I do further research.