Northwest corner. Small marble obelisk. No inscriptioin. Identical obelisk may have been intended for wife.
Source: Hancock County [Illinois] Cemeteries, vol. 8, Providence Cemetery, Saint Marys Township, list prepared 1965 by Miss Mary Siegfried and typed by Warren VanDine, copy at the Illinois Historical Library, Springfield, IL.

NOTE: He was married 25 Jun 1863 to Mary Elizabeth Polk in Hancock Co., IL
Found in online marriage indexes, Illinois State Archives, Springfield, IL:
Wilson, Aris, to Polk, Mary, 25 Jun 1863, v4 p5, #1392, Hancock Co, IL.

1870 - M593_227, Plymouth, St Mary Twp, Hancock Co, IL, line 12, page 350A, 20 Jul 1870
[Ancestry.com, image
Wilson, Arias [smudged], 29, male, white, farmer, VA
Wilson, May E, 29, female, white, keeping house, IL
Wilson, William E, 6, male, white, IL

1880 - T9-0211, St Marys Twp, Hancock Co, IL, ED 82, line 7, page 307A, 21 Jun 1880
[Ancestry.com, image 25 of 32]
Wilson, Aris, white, male, 40, self, married, farmer, born VA, parents born VA
Wilson, Mary E, white, female, 40, wife, married, keeping house, born IN, parents born
Wilson, William A, white, male, 16, son, single, farm hand, born IL, father born VA, mother born IL
Wilson, Lula C, white, female, 3, daughter, single, born IL, father born VA, mother born IL

1900 - T623_305, St Mary Twp, Hancock Co, IL, ED 32, line 19, page 269A (6A), 20 Jun 1900
[Ancestry.com, image
Wilson, Aris, head, white, male, May 1841, 59, married 36 years, VA, VA, VA, farmer
Wilson, Mary E, wife, white, female, Dec 1840, 59, married 36 years, IN, IN, IN

1910 - T624_290, St Mary Twp, Hancock Co, IL, ED 24, line 85, 273B (13B), 3rd & 4th May 1910
[Ancestry.com, image 26 of 33]
Wilson, Aris, head, male, white, 68, married once 46 years, born VA, parents born VA, own income
Wilson, Mary E, wife, female, white, 69, married once 46 years, 3 children, 1 living, born IN, parents born IN