At Gettysburg, the 66th New York Infantry served as a member of Zook’s Brigade in Caldwell’s Division of the Second Corps, Army of the Potomac. The regiment was recruited at New York City (a few men were from New Jersey), and there mustered in the service of the United States for three years November 4, 1861. The infantry mustered out on August 30, 1863. During its service the regiment lost by death, killed in action, 8 officers, 60 enlisted men- of wounds received in action, 2 officers, 37 enlisted men; of disease and other causes, 4 officers, 120 enlisted men; total, 14 officers, 217 enlisted men; aggregate, 231; of whom 2 officers, 54 enlisted men died in the hands of the enemy. The infantry was commanded by Colonel Orlando H. Morris (1835-1864), a graduate of Columbia and a lawyer in New York City. Morris was wounded on July 2d carrying the regimental colors and eventually killed in action at Cold Harbor on June 3, 1864. Under his command, the 66th brought 176 men to the Gettysburg Battlefield and among them 5 were killed, 29 were wounded and 10 men went missing.
The 66th New York Infantry Monument is located on the right or north side of Sickles Avenue while traveling northwest. The monument is just before the beginning of The Loop. aptly named considering the road looks like a teardrop. The 
Irish Brigade Monument (MN156-A) is directly across the road and the 5th Michigan Infantry Monument (MN154) is 40 feet south or to the right. This area is heavily wooded. There are also a tremendous amount of monuments here as well. Parking is available along the side of the road at intermittently enlarged shoulders. Take care to park in the white lines or on asphalt widened shoulders and not park on anything remotely green looking as Park Police will happily ticket you. I visited this site on Monday, July 1, 2013 on the 150th anniversary of the Battle of Gettysburg @ 5:30 PM, EDT & @ an altitude of 546 feet, ASL. As always, I used my trusty and oft abused Canon PowerShot 14.1 Megapixel, SX210 IS digital camera for the photos.
The Draw the Sword site helped out by the NPS narrative and the SIRIS site offers the following description: The monument was paid for using the state appropriation of $1,500.00. Granite shaft with apex cap, and bronze adornments, including a trefoil design and state tondo on one side; and a relief depicting Union soldier sharing canteen and shaking hands with a Confederate soldier under a banner inscribed Peace and Unity. Monument is a granite shaft topped with a cornice and apex cap set on a 7×6.3 foot rough and smooth double base. Overall height is 13.9 foot. The shaft has a bronze trefoil and state seal on the east face and a bronze relief on the west side.
The 66th New York Infantry Monument was dedicated on October 9, 1889 by the State of New York. The sculpture is composed of Hallowell granite save for the bronze used for the adornment. Overall, the monument is approximately 12 feet x 5 feet 10 inches x 5 feet 1 inch. The monument was sculpted by Maurice J. Power (1838 - 1902). There is a single inscription on the front recalls the order of battle and casualties and reads:
66th New York
Infantry;
3rd Brigade,
1st Division,
2nd Corps.
July 2, 1863.
6 p.m.
Casualties:
5 killed,
29 wounded.
10 missing.
The 66th New York Infantry Monument is a contributing feature to the Gettysburg National Military Park Historic District which is nationally significant under NR Criteria A, B, C & D. Areas of Significance: Military, Politics/Government, Landscape Architecture, Conservation, Archeology-Historic. Period of Significance: 1863-1938. The original National Register Nomination was approved by the Keeper March 19, 1975. An update to this nomination was approved by the Keeper on January 23, 2004. The monument is identified as structure number MN155.
From the Nomination Form:
1 of 90 mns in Park to NY commands in Gettysburg Campaign. Marks position reached by 66 NY on July 2, 1863 in their "victorious advance" across Wheatfield to ravine of Rose Farm. Located on N side of Sickles Ave at Loop.
Short Physical Description:
Rough & smooth double-base, 7'x6'3". Granite shaft topped w/ cornice & apex cap. All 13'9"H. Shaft has bronze trefoil & state seal on E. face, Bronze relief, 2'x4' on W.
Long Physical Description:
Monument is a granite shaft topped with a cornice and apex cap set on a 7x6.3 foot rough and smooth double base. Overall height is 13.9 foot. The shaft has a bronze trefoil and state seal on the east face and a bronze relief on the west side. Designed by Bryon J. Picket. Located on the north side of Sickles Avenue at the Loop.
My Sources
1.
NRHP Nomination Form
2.
SIRIS
3.
Stone Sentinels
4.
Virtual Gettysburg
5.
Draw the Sword
6.
Historical Marker Database
7.
New York State Military Museum