The 3rd Maine Infantry served as a member of Ward’s Brigade in Birney’s Division of the Third Corps, Army of the Potomac, a Fighting 300 Regiment. The unit was commanded by Colonel Moses B. Lakeman (1828-1907). Lakeman took over the brigade on July 3rd, and Captain William C. Morgan took command of the regiment. The unit has 266 men engaed at Gettysburg with 18 killed, 59 wounded and 45 who went missing.
The 3rd Maine Infantry Monument just off of Route 15, part of the newly adopted Pennsylvania Byway system, at the southwest corner of the Peach Orchard.. Traveling south down Rt. 15, make a left on Birney Avenue. The monument is 31 feet off to the left or northeast side of the road, directly to the right of the 2nd New Hampshire Infantry Monument (MN176-B). The monument is 138 feet from the Emmitsburg Road (Business U.S. 15) intersection (actually a "T"). 
Parking is available at small, cutout shoulders along the road, some wide, some narrow. Be sure to stay off the grass or you will be tickete by park police. I visited this monument on Thursday, July 5, 2012 at 11:32 AM. I was at an elevation of 616 feet, ASL. I used my Canon PowerShot 14.1 Megapixel, SX210 IS digital camera for my photos.
The Draw the Sword site helped out by the NPS narrative and the SIRIS site offers the following description: Granite monument, primarily rock-faced with inscriptions incised into smooth-faced panels on sides of shaft. The monument has a tapering shaft and diamond-shaped finial and is set atop a two-tiered base. Monument is a 2.6 foot tapering granite shaft that is 8.1 foot high and topped with an inverted 3rd Corps Diamond Lozenge set on a 5.5×1.6 foot rough hewn base. The shaft has polished inscription panels on the north and south sides. Overall height is 13.1 foot. Flanking markers are one foot square. The monument marks the line held by the 3rd Maine Infantry in the Sherfy Peach Orchard, on the afternoon of July 2, 1863.
The monument was erected on October 23, 1889 by the State of Maine. The base of the monument is of granite and the sculpture is of marble. The granite monument's dimensions are approximately 13 ft. 1 in. x 5 ft. x 5 ft. I could not find out who sculpted or fabricated the monument. There are inscriptions on the front and left sides which reads:
(Front):3rd
Maine Inft'y
2nd Brigade
1st Division
3rd Corps
Strength of regiment
morning of July 2nd
14 officers and 196 men
(Left):
Detached from the Brigade. Fought here in the afternoon of July 2nd, 1863. Having been engaged in the forenoon at point in advance as indicated by a marker.————
July 3rdin position on left centre of line, until afternoon, when with other regiments of the Brigade, it moved to support of the centre at time of the enemy's assault.————1 officer and 17 men killed, 2 officers and 57 men wounded, 45 men missing.
The 3rd Maine 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 MN177-D.
From the Nomination Form:
1 of 15 mns in Park honoring Maine commands. Marks where regiment was engaged on July 2, 1863, at SW corner of Peach Orchard. Pitzer Woods position marker on Berdan Av marks morning of July 2. E side of Hancock Ave marker marks regiment on July 3.
Short Physical Description:
Mn, 2 flank & 2 position markers. Mn: Rough-hewn base, 5'x5'x1'6" & tappering granite shaft, 2'6" sq 8'1" high, topped w/inverted Corps Diamond Lozenge. Polished inscription panels on N & S side of shaft Overall 13'1" high. Position markers, 2'x2'x2'. Flank markers, 1'x1'x2'.
Long Physical Description:
Monument that has two flanking markers and two position markers. Monument is a 2.6 foot tapering granite shaft that is 8.1 foot high and topped with an inverted 3rd Corps Diamond Lozenge set on a 5.5x1.6 foot rough hewn base. The shaft has polished inscription panels on the north and south sides. Overall height is 13.1 foot. Flanking markers are one foot square. Position markers are two foot square. Monument located at the southwest corner of the Peach Orchard. One position marker located in Pitzer Woods on Berdan Avenue and the other position marker is found on the east side of Hancock Avenue.
My Sources
1.
NRHP Nomination Form
2.
SIRIS
3.
Stone Sentinels
4.
Virtual Gettysburg
5.
Draw the Sword
6.
Historical Marker Database
7.
Find A Grave