Following up on my earlier post on the Roosevelt family, I noted that Presidents Theodore and Franklin Roosevelt’s kinship by marriage was the closer way they connected, as their closest kinship by blood was that of fifth cousins. (Their last common Roosevelt ancestors in New York City were in the early eighteenth century.)
While it is common knowledge that the Roosevelts were distant cousins, after the Adams and Bush father and son presidents, and the Harrison grandfather and grandson presidents, there are several sets of presidential kinships that are closer than the fifth cousin kinship of the Roosevelts – most are at a few generations removed, but they begin at a closer “base” level of cousinship. James Madison and Zachary Taylor are first, second cousins through their common Taylor ancestors of Virginia, as well as second cousins twice removed through their Thornton ancestors.
After that, there are several other kinships between American presidents that are closer than fifth cousins, through common American ancestors, all outlined in charts in Ancestors of American Presidents (AAP) (only the closest kinship between two presidents is given below):
Second cousins four times removed: Martin Van Buren and Theodore Roosevelt (AAP, p. 514), through Claes Laurenszen Van Schaack and Jannetje Cornelis of Kinderhook, New York.
Second cousins six times removed: Franklin Pierce and George W. Bush (AAP, p. 517), through Thomas and Elizabeth (Cole) Pierce of Woburn, Massachusetts (an ancestor of Barbara [Pierce] Bush).
Third cousins four times removed: Martin Van Buren and Franklin Delano Roosevelt (AAP, p. 570), through Teuwis Abrahamsz van Deursen and Helena Robberts of Albany, New York.
Third cousins five times removed: John Adams and Calvin Coolidge (AAP, p. 465), through Mayflower passengers John and Priscilla (Mullins) Alden of Duxbury, Massachusetts.
Third cousins nine times removed: James Madison and Barack Obama (AAP, p. 569), through Edwin and Martha (Eltonhead) Conway of Lancaster County, Virginia.
Fourth cousins once removed: William Henry Harrison and John Tyler (p. 471), through William and Ann (Ellis) Armistead of Elizabeth City County, Virginia; Ulysses Grant and Franklin Delano Roosevelt (AAP, pp. 520-21), through Jonathan and Mercy (Delano) Warren of Dartmouth, Massachusetts.
Obviously, most of these closer kinships contain at least one earlier president who had fewer ancestral generations in the present-day United States.
Fourth cousins three times removed: Lyndon Johnson and Barack Obama (AAP, p. 587), through Philip and Maria Elisabeth (Schmid) Ament of Bourbon County, Kentucky.
Fourth cousins four times removed: John Quincy Adams and Calvin Coolidge (AAP, p. 465), through Mayflower passengers John and Priscilla (Mullins) Alden of Duxbury, Massachusetts.; Franklin Pierce and Calvin Coolidge (AAP, p. 478), through John and Dorcas (_____) Pearson of Rowley, Massachusetts; Zachary Taylor and Jimmy Carter (AAP, p. 572), probably, through William and Dorothy (_____) Strother of Richmond County, Virginia.
Fourth cousins five times removed: Millard Fillmore and George H.W. Bush (AAP, p. 477), through Robert and Elizabeth (Sabin) Millard of Rehoboth, Massachusetts; Franklin Pierce and Herbert Hoover (AAP, p. 478), through John and Dorcas (_____) Pearson of Rowley, Massachusetts; James Madison and Theodore Roosevelt (AAP, p. 568), probably, through _____ and Margaret (_____) Underwood of Rappahannock Co., Virginia.
Fourth cousins six times removed: Millard Fillmore and George W. Bush (AAP, p. 477), through Robert and Elizabeth (Sabin) Millard of Rehoboth, Massachusetts.
Fourth cousins of the half blood, three times removed: Zachary Taylor and Franklin Delano Roosevelt (AAP, p. 571), through Mayflower passenger Isaac Allerton of Plymouth, Massachusetts.
Obviously, most of these closer kinships contain at least one earlier president who had fewer ancestral generations in the present-day United States. The same would be for anyone distantly related to a president through colonial American ancestors. My closest kinship is to John Adams at third cousins eight times removed (through Samuel and Anne [Savell] Bass, AAP, pp. 466-67), followed by both John Quincy Adams and Franklin Pierce at fourth cousins six times removed (for J.Q. Adams through Henry and Anna [Goldstone] Bright, and for Pierce through Henry and Elizabeth [Johnson] Bowen). Your kinships to modern presidents are likely much more distant; my own most distant American kinship to an American president is as a twelfth cousin of the half-blood to Obama through our shared descent from George Allen of Sandwich, Massachusetts. George Allen is also an ancestor of Gerald Ford through George’s same daughter Rose (Allen) Holley, making Ford and Obama eleventh cousins once removed (AAP, p. 588), which I believe is the most distant kinship between two presidents through a shared American ancestor.
 Gerald Ford and George W. Bush are also eleventh cousins once removed through their shared descent from Edward Gilman (bp. 1557) and his unknown wife of Hingham, Norfolk, England (AAP, p. 453). However, this descent is through an ancestor who died in England, as his children were the immigrants to America. Also on AAP, 461 is a Stan(d)ley chart showing Ford and G.W. Bush as twelfth cousins, but this again is through ancestors who died in England who were the parents and grandparents of a few American immigrants. There are a few other kinships at this level or more distant in AAP, but all through common ancestors who had died in England.