"Sheridan's Trevillian Raid June 7-24. Elliott's Mills June 8. Trevillian Station June 11-12. Black Creek, Tunstall Station, June 21. White House, St. Peter's Church, June 21. St. Mary's Church June 24"

From: The Civil War, DAy by Day
June 24, 1864 - Friday
At St. Mary's Church, Va, Confederate cavalry attacked Sheridan and the wagon train heading from White House, Va to the James River. Federal cavalry fell back in considerable confusion.

I don't know what to tell you on this one. I grew up in the area and I have never heard of a "St. Mary's Church, VA". But from what was written, I would think it was probably in Henrico county and may no longer exist. St. Peter's Church is near Tallysville in New Kent County, Va. [Va 249 at Va 106]. A two day wagon trip from that point towards the James River would put you in Henrico County.

Go to this site to see the whole report:
http://alkmene.perseus.tufts.edu/hopper/text.jsp?doc=Perseus:text:2001.05.0035:chapter=22

Philip Henry Sheridan, Personal Memoirs of P. H. Sheridan, General, United States Army .

While at the White House I received orders to break up that depot wholly, and also instructions to move the trains which the Army of the Potomac had left there across the peninsula to the pontoon-bridge at Ieep Bottom on the James River. These trains amounted to hundreds of wagons and other vehicles, and knowing full well the dangers which would attend the difficult problem of getting them over to Petersburg, I decided to start them with as little delay as circumstances would permit, and the morning of the 22d sent Torbert's division ahead to secure Jones's bridge on the Chickahominy, so that the wagons could be crossed at that point. The trains followed Torbert, while Gregg's division [234] marched by a road parallel to the one on which the wagons were moving, and on their right flank, as they needed to be covered and protected in that direction only.

The enemy made no effort to attack us while we were moving the trains that day, and the wagons were all safely parked for the night on the south side of the Chickahominy, guarded by General Getty, who had relieved Abercrombie from command of the infantry fragments before we started off from the White House.

To secure the crossing at Jones's bridge, Torbert had pushed Devin's brigade out on the Long Bridge road, on the side of the Chickahominy where, on the morning of the 23d, he was attacked by Chambliss's brigade of W. H. F. Lee's division. Devin was driven in some little distance, but being reinforced by Getty with six companies of colored troops, he quickly turned the tables on Chambliss and re-established his picket-posts. From this affair I learned that Chambliss's brigade was the advance of the Confederate cavalry corps, while Hampton discovered from it that we were already in possession of the Jones's bridge crossing of the Chickahominy; and as he was too late to challenge our passage of the stream at this point he contented himself with taking up a position that night so as to cover the roads leading from Long Bridge to Westover, with the purpose of preventing the trains from following the river road to the pontoon-bridge at Deep Bottom.

My instructions required me to cross the trains over the James River on this pontoon-bridge if practicable, and to reach it I should be obliged to march through Charles City Court House, and then by Harrison's Landing and Malvern Hill, the latter point being held by the enemy. In fact, he held all the ground between Long Bridge on the Chickahominy and the pontoon-bridge except the tete de pont at the crossing. Notwithstanding this I concluded to make the attempt, for all the delays of ferrying the command and trains would be avoided if we got through to the bridge; and with this object in view I moved Torbert's division out on the Charles City road to conduct the wagons. Just beyond Charles City Court House Torbert encountered Lomax's brigade, which he drove across Herring Creek on the road to Westover Church; and reporting the affair to me, I surmised, from the presence of this force in my front, that Hampton would endeavor to penetrate to the long column of wagons, so I ordered them to go into park near Wilcox's landing, and instructed Gregg, whose division had been marching in the morning along the road leading from Jones's bridge to St. Mary's Church for the purpose of covering the exposed flank of the train, to hold fast near the church without fail till all the transportation had passed Charles City Court House. [235]

Meanwhile, General Hampton, who had conjectured that I would try to get the train across the James by the pontoon-bridge at Deep Bottom, began concentrating all his troops except Lomax's brigade, which was to confront the head of my column on the river road, in the vicinity of Nance's Shop. This was discovered by Gregg at an early hour, and divining this purpose he had prepared to meet it by constructing hasty cover for his men before receiving my instructions. About 4 o'clock in the afternoon Hampton got his force in hand, and with Fitzhugh Lee's division assailed the whole front of Gregg's line, and his left flank with Chambliss's and Geary's brigades. For two hours he continued to attack, but made little impression on Gregg-gain at one point being counterbalanced by failure at another. Because of the evident strength of Hampton, Gregg had placed all his troops in line of battle from the first, and on discovery of the enemy's superior numbers sent message after message to me concerning the situation, but the messengers never arrived, being either killed or captured, and I remained in total ignorance till dark of the strait his division was in.

Toward night it became clear to Gregg that he could maintain the unequal contest no longer, and he then decided to retreat, but not until convinced that the time won had enabled all the trains to pass Charles City Court House in safety. When he had got all his led horses fairly on the way, and such of the wounded as could be transported, he retired by his right flank — in some confusion, it is true, but stubbornly resisting — to Hopewell Church, where Hampton ceased to press him.

Gregg's losses were heavy, and he was forced to abandon his dead and most seriously wounded, but the creditable stand made ensured the safety of the train, the last wagon of which was now parked at Wilcox's Landing. His steady, unflinching determination to gain time for the wagons to get beyond the point of danger was characteristic of the man, and this was the third occasion on which he had exhibited a high order of capacity and sound judgment since coming under my command. The firmness and coolness with which he always met the responsibilities of a dangerous place were particularly strong points in Gregg's make-up, and he possessed so much professional though unpretentious ability, that it is to be regretted he felt obliged a few months later to quit the service before the close of the war.

Gregg's fight fully satisfied me that we could not get the trains up to the pontoon-bridge, for of course Hampton would now throw all his cavalry in my front, on the river road, where it could be backed up by Lee's infantry. Meanwhile, General Meade had become assured of the same thing, and as he was now growing anxious about the fate of Wilson's [237] division-which, during my absence, had been sent out to break the enemy's communications south of Petersburg, by destroying the Southside and Danville railroads-he sent ferryboats to cross me over the James. During the night of the 24th, and next morning, the immense train — which ought never to have been left for the cavalry to escort, after a fatiguing expedition of three weeks--was moved back through Charles City Court House to Douthard's landing, and there ferried over the river, followed by my troops in like manner. When General Hampton discovered this, he moved to Drury's Bluff, and there, on the morning of the 27th, crossed the James by the Confederate pontoon-bridge.

This seems to put St Mary's Church on Va 155 in Charles City County.

http://www.perseus.tufts.edu/cgi-bin/image?lookup=Perseus:text:2001.05.0035.fig00235