Charles Henry Tucker "Tucky" Collis (February 4, 1838 - May 11, 1902) was an Irish-American US Army officer who received the Medal of Honor for his actions in the American Civil War. He was born in Ireland. On December 12, 1864, President Abraham Lincoln nominated Collis for appointment to the brevet grade of brigadier general of volunteers to rank from October 28, 1864 and the U.S. Senate confirmed the appointment on February 14, 1865. Following the war, Collis returned to practicing law, becoming an Assistant City Solicitor in Philadelphia. Collis died at Bryn Mawr, Pennsylvania on May 11, 1902. He was buried at Gettysburg National Cemetery.
After the war Collis built a summer house in Gettysburg which still stands on Seminary Ridge just off the Fairfield Road at the beginning of West Confederate Avenue. The cottage, named "Red Patch" after the 3rd Corps symbol, has bedrooms named after Union generals. SOURCE
The memorial is located inside the National Cemetery. One would go in through the Baltimore Pike entrance and stay to the right, following the path, going past the New York monument. Soon you will see sections of graves for individual states. It is 214 west of the National monument and 214 feet east of the Taneytown Rad wall. 
Parking is available in front of the cemetery at metered spots along the curb. There is also a lot located to the left of East Cemetery Hill (if facing it) in a tourist-tour business that always has space. I visited this site on Monday, July 1, 2013 on the 150th anniversary of the Battle of Gettysburg @ 11:47 AM, EDT & @ an altitude of 606 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: Bust of Charles Collis stands on a pedestal which is placed in the center of a two-stepped exedra. The figure wears a double-breasted military uniform and has short hair and a mustache. Sculpture was erected by surviving members of the 114th Pennsylvania Regiment and by friends of Charles Collis (1838-1902) after his death. Colonel Collis was the commander of the regiment, also known as “Collis Zouaves.” The regiment fought the battle in the Peach Orchard on the second day of the Gettysburg battle. He resided in Gettysburg after the war and his house, Red Patch, still stands. This is the only personal memorial erected within the Civil War interment section. Special authorization for the memorial was granted by the Secretary of War.
This monument was dedicated on May 13, 1906 by the survivors of his regiment and his friends. The monument is composed of granite (with bronze used for the beautiful relief tablets) and has the following dimensions: The sculpture is approximately 2' x 2' x 1.5 feet and the base is approximately 4' x 8' x 3'. I was not able to recover information about the artist. There is an inscription on the front which reads:
Bt. Maj. Gen.
Chas. H. T. Collis. U.S.V.
Col. 114 Reg't Penn'a Vol. Infty.
Collis Zouaves
Born Feb. 4, 1838 Died May 11, 1902
Erected by the
Survivors of his regiment
and his friends.
The Brevet Major General Charles H. T. Collis Memorial 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 MN406.
From the Nomination Form:
Memorial is to Collis, commander of the 114th Pennsylvania Volunteers and recipient of the Medal of Honor. The only personal memorial erected within the Civil War interment section. Special authorization for the memorial was granted by the Secretary of War. Located in National Cemetery by PA graves.
Short Physical Description:
It is a simple granite exedra approached by two granite steps and broken by a central pedestal upon which a bronze bust of Collis in a Zouave uniform is mounted. A bronze diamond-shaped tablet on the pedestal bears an inscription to Collis.10'8"Lx4'Wx7'8"H (overall), 4'x4'x7'8" (shaft).
Long Physical Description:
This memorial is to Collis, commander of the 114th Pennsylvania Volunteers and recipient of the Medal of Honor. It is a simple granite exedra approached by two granite steps and broken by a central pedestal upon which a bronze bust of Collis in a Zouave uniform is mounted. A bronze diamond-shaped tablet on the pedestal bears an inscription to Collis. This is the only personal memorial erected within the Civil War interment section. Special authorization for the memorial was granted by the Secretary of War.
My Sources
1.
NRHP Nomination Form
2.
SIRIS
3.
Stone Sentinels
4.
Virtual Gettysburg
5.
Draw the Sword
6.
Historical Marker Database
7.
Wikipedia