From Wikipedia on the various units:
11th:
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13th:
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15th:
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16th:
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"The 11th Iowa Infantry was organized at Davenport, Iowa and mustered into Federal service between September 28 and October 18, 1861. The regiment was mustered out on July 15, 1865.
"Total enrollment was 1297. The regiment lost 5 officers and 86 enlisted men who were killed in action or who died of their wounds and 2 officers and 166 enlisted men who died of disease, for a total of 259 fatalities. 234 were wounded.
"The 13th Iowa Infantry was organized at Davenport, Iowa and mustered in for three years of Federal service between October 18 and November 2, 1861. Its troops came primarily from the Iowa counties of Linn, Jasper, Marion, Lucas, Keokuk, Scott, Polk, Benton, Marshall and Washington.
The regiment was mustered out on July 21, 1865.
The 13th Iowa mustered 1788 men at one time or another during its existence. It suffered 5 officers and 114 enlisted men who were killed in action or who died of their wounds and 4 officers and 205 enlisted men who died of disease, for a total of 328 fatalities."
"The 15th Iowa Infantry was organized at Keokuk, Iowa and mustered in for three years of Federal service on February 22, 1862.
The regiment was mustered out on July 24, 1865.
The 15th Iowa mustered a total of 1,926 men over the span of its existence. It suffered 8 officers and 118 enlisted men who were killed in action or who died of their wounds and 1 officer and 260 enlisted men who died of disease, for a total of 387 fatalities."
"The 16th Iowa Infantry was organized at Davenport, Iowa and mustered in for three years of Federal service by companies between December 10, 1861 and March 12, 1862.
The regiment was mustered out on July 19, 1865.
The 16th Iowa mustered a total of 1,441 men over the span of its existence. Seven officers and 94 enlisted men were killed in action or died of their wounds, while three officers and 219 enlisted men died of disease, for a total of 323 fatalities."
Text of the marker:
(shield with olive branches)
IOWA
11, 13, 15, and 16th Infantry
(Skirmishers)
3d Brig. 6th Div. 17th Corps
Assault May 22 1863
Casualties
Killed 1 Wounded 2 Total 3 (11th Killed 1
Wounded 1 Total 2 16th Wounded 1)