I know some of this family very well and as you suggest they are from the Indiana/Illinois area.Below is enough information to take your family line all the way back to the first Cornelius Evertsz Wijnkoop who arrived in this country in 1651:
Descendants of Garrett Wynkoop
Generation No. 1
1.GARRETT6 WYNKOOP(ADRIAN5, GERRIT4, GERRET3, CORNELIUS EVERTSZ2, EVERT1) was born Bet. 1771 - 1780 in Bucks County, Pennsylvania.He married SARAH MARTIN.She was born Bet. 1781 - 1790 in Bucks County, Pennsylvania.
Children of GARRETT WYNKOOP and SARAH MARTIN are:
i. ADRIAN7 WYNKOOP.
2. ii. WILLIAM M. WYNEKOOP, b. Abt. 1802, Frederick County, Virginia.
iii. MARGARET WYNKOOP, m. NATHAN HENDRICKS.
iv. ELIZABETH WYNKOOP.
v. JEPHTHAH WYNKOOP.
vi. MARY WYNKOOP, m. GEORGE RANDELL.
vii. JOHN WYNKOOP, m. MARGARET PIPER.
3. viii. GARRET WYNKOOP, b. Bet. 1781 - 1790.
Generation No. 2
2.WILLIAM M.7 WYNEKOOP (GARRETT6 WYNKOOP, ADRIAN5, GERRIT4, GERRET3, CORNELIUS EVERTSZ2, EVERT1) was born Abt. 1802 in Frederick County, Virginia.He married ELIZABETH A. VAN METRE Bef. 1829.She was born 1806 in Virginia.
Children of WILLIAM WYNEKOOP and ELIZABETH VAN METRE are:
i. JAMES M.8 WYNEKOOP, b. 1829, Indiana; m. MINERVA J.; b. 1835, Indiana.
ii. NATHAN WYNEKOOP, b. 1831, Indiana.
iii. JOHN WYNEKOOP, b. 1834, Indiana.
iv. MARY L. WYNEKOOP, b. 1834, Indiana.
4. v. WILLIAM WYNEKOOP, b. 1835, Indiana.
vi. SARAH WYNEKOOP, b. 1838, Indiana.
vii. HADEN WYNEKOOP, b. 1842, Indiana.
viii. MARY WYNEKOOP, b. 1843, Indiana.
ix. ANN WYNEKOOP, b. 1844, Indiana.
x. ELIZA I. WYNEKOOP, b. 1844, Indiana.
xi. EMMA WYNEKOOP, b. 1846, Indiana.
xii. HENRY WYNEKOOP, b. 1848, Indiana.
xiii. NAOMI WYNEKOOP, b. 1849, Indiana.
xiv. MINERVA A. WYNEKOOP, b. 1858, Indiana.
3.GARRET7 WYNKOOP (GARRETT6, ADRIAN5, GERRIT4, GERRET3, CORNELIUS EVERTSZ2, EVERT1) was born Bet. 1781 - 1790.He married JULIA ADELAIDE MOUNTZ 1841, daughter of JACOB MOUNTZ and PAMELIA.She was born Bet. 1791 - 1800, and died October 26, 1872.
Children of GARRET WYNKOOP and JULIA MOUNTZ are:
i. PAMELIA WINTER8 WYNKOOP.
ii. MARY EMMA WYNKOOP.
iii. ADRIAN GARRET WYNKOOP.
iv. JULIA ADELAIDE WYNKOOP.
v. CLARA VIRGINIA WYNKOOP.
vi. WILLIAM HAMILTON WYNKOOP.
Generation No. 3
4.WILLIAM8 WYNEKOOP (WILLIAM M.7, GARRETT6 WYNKOOP, ADRIAN5, GERRIT4, GERRET3, CORNELIUS EVERTSZ2, EVERT1) was born 1835 in Indiana.He married HELLEN M. HAYNES 1865, daughter of HAYNES and UNKNOWN.She was born August 1846 in Ohio.
Children of WILLIAM WYNEKOOP and HELLEN HAYNES are:
5. i. FRANK ELDRIDGE9 WYNEKOOP, M.D., b. December 1866, Indiana; d. Bef. November 21, 1933, Illinois.
ii. LORETTA E. WYNEKOOP, b. 1869, Indiana.
6. iii. HARVEY E. WYNEKOOP, b. October 1869, Indiana.
iv. CHARLES IRA WYNEKOOP, M.D., b. January 1872, Indiana; m. JOSEPHINE C.; b. 1873, Illinois.
7. v. ELIDE WYNEKOOP, b. 1875, Indiana.
vi. CARRIE C. WYNEKOOP, b. March 1875, Indiana.
8. vii. FLORENCE WYNEKOOP, b. 1877, Indiana.
9. viii. GILBERT H. WYNEKOOP, M.D., b. November 1879, Indiana.
Generation No. 4
5.FRANK ELDRIDGE9 WYNEKOOP, M.D. (WILLIAM8, WILLIAM M.7, GARRETT6 WYNKOOP, ADRIAN5, GERRIT4, GERRET3, CORNELIUS EVERTSZ2, EVERT1) was born December 1866 in Indiana, and died Bef. November 21, 1933 in Illinois.He married DR. ALICE LOIS LINDSAY, M.D. April 17, 1900 in Iroquois County, Illinois, daughter of LINDSAY and WIFE.She was born November 1867 in Illinois, and died July 04, 1955 in Chicago, Cook County, Illinois.
Children of FRANK WYNEKOOP and ALICE LINDSAY are:
i. FRANK10 WYNEKOOP.
ii. WALKER WYNEKOOP.
iii. JAMES EARLE WYNEKOOP, m. RHETA GARDNER; d. November 21, 1933, Chicago, Cook County, Illinois.
iv. DR. CATHERINE WYNEKOOP, M.D..
6.HARVEY E.9 WYNEKOOP (WILLIAM8, WILLIAM M.7, GARRETT6 WYNKOOP, ADRIAN5, GERRIT4, GERRET3, CORNELIUS EVERTSZ2, EVERT1) was born October 1869 in Indiana.He married HENRIETTA WYMAN 1899, daughter of WYMAN and KATHERINE.She was born March 1874 in Indiana.
Children of HARVEY WYNEKOOP and HENRIETTA WYMAN are:
i. WALDO W.10 WYNEKOOP, b. September 29, 1902, Illinois; d. June 08, 1989, Bellflower, Los Angeles, California.
ii. GARRETT A. WYNEKOOP, b. 1915, Illinois.
7.ELIDE9 WYNEKOOP (WILLIAM8, WILLIAM M.7, GARRETT6 WYNKOOP, ADRIAN5, GERRIT4, GERRET3, CORNELIUS EVERTSZ2, EVERT1) was born 1875 in Indiana.She married BAYNE.
Child of ELIDE WYNEKOOP and BAYNE is:
i. PAULE10 BAYNE.
8.FLORENCE9 WYNEKOOP (WILLIAM8, WILLIAM M.7, GARRETT6 WYNKOOP, ADRIAN5, GERRIT4, GERRET3, CORNELIUS EVERTSZ2, EVERT1) was born 1877 in Indiana.She married SETH WICKS, M.D..
Child of FLORENCE WYNEKOOP and SETH WICKS is:
i. SON10 WICKS, M.D..
9.GILBERT H.9 WYNEKOOP, M.D. (WILLIAM8, WILLIAM M.7, GARRETT6 WYNKOOP, ADRIAN5, GERRIT4, GERRET3, CORNELIUS EVERTSZ2, EVERT1) was born November 1879 in Indiana.He married LUCIL MOLLIE M..She was born 1892 in Indiana.
Child of GILBERT WYNEKOOP and LUCIL M. is:
i. GIPSEY L.10 WYNEKOOP, b. September 14, 1914, Illinois; d. November 29, 1994.
You can find all four versions of Richard Wynkoop's "Wynkoop Genealogies" at my website:
I would really like to talk to you about this family as obviously I've done quite a bit of research on them.I have more information on them that I could share by email if you'd like to contact me at:
I'm really looking forward to talking to you.Hope the above information whets your appetite.