Richard Wynkoop, in the 1904 edition of the Wynkoop Genealogy in the United States of America, has this to say about him on page 184:

    1162. William Wynkoop, Captain, (Thomas L. 681, William 375, Gerardus 153, Gerrit 45, Gerret 5, Cornelius 1,) born July 1, 1835: married, January 6, 1859, Rachel A. Blaker, born March 22, 1841, daughter of Joshua Carson and Anne (Cevasdale) Blaker.
    He enlisted, August 5, 1861, as private in the 1st Reg. N. Y. Cavalry: was promoted to 1st sergeantcy, 2d lieutenantcy, 1st lieutenantcy, and captaincy: he was on the staff of Brig.-Gen'l Davies, serving as provost marshall, aide-de-camp, and acting assistant adjutant-general: he was wounded in the ear, and on May 28, 1864, near Salem Court House, Va., in the foot: was honorably discharged, September 26, 1864.
    He was a planter, at Newtown, Bucks County, Penn.: an elder in the Presbyterian church, and superintendent of the Sabbath school, from 1872. In 1884, he was a commissioner to the Presbyterian General Assembly, at Madison, Wis.; and, in 1890, to the General Assembly, at Saratoga, N. Y. He lives in Newtown.
    Children of Capt. William and Rachel A. Wynkoop:
1582. Annie Blaker: b. Feb. 4, 1860: died, aged about 19.
1583. Elizabeth Torbert: b. Mch. 28, 1861: m. George Luff.
1584. Catharine Vansant: b. Feb. 28, 1864: m. Henry Conklin Wylie, who d. about 1891. He was in business in New York, and lived in Rutherford, N. J.
1585. Eva Blaker.
1586. James Anthony.

Grant! Details of the Fighting.
     Lt. William Wynkoop participates in the fighting around Dabney ferry, on the Pamunkey River in Virginia, from the New York Herald, Thursday, 2 June 1864.

Captain William Wynkoop.
     William W. H. Davis's biography of the Civil War soldier from the History of Bucks County, Pennsylvania, Volume III.

Captain William Wynkoop and His Company "A".
     A Biography of the Civil War soldier by Thaddeus S. Kenderdine.

The Wynkoop Family by Captain William Wynkoop
    A speech delivered May 27, 1902 to the Bucks County Historical Society.