On 05 Jan 1769 Charles Sackville 2nd Duke Dorset 1711-1769 (age 57) died. His nephew [her father] John Frederick Sackville 3rd Duke Dorset (age 23) succeeded 3rd Duke Dorset, 9th Earl Dorset, 4th Earl Middlesex, 9th Baron Buckhurst, 4th Baron Cranfield of Cranfield in Middlesex.
In 1790 [her father] John Frederick Sackville 3rd Duke Dorset (age 44) and [her mother] Arabella Diana Cope 3rd Duchess Dorset 1769-1825 (age 21) were married. She by marriage Duchess Dorset, 9th Countess Dorset. The difference in their ages was 23 years. She the daughter of Charles Cope 2nd Baronet and Catherine Bisshopp Countess Liverpool (age 45).
On 30 Jul 1792 Mary Sackville Countess Plymouth Amherst was born to John Frederick Sackville 3rd Duke Dorset (age 47) and Arabella Diana Cope 3rd Duchess Dorset 1769-1825 (age 23).
On 12 Jun 1799 Other Windsor 5th Earl Plymouth 1751-1799 (age 48) died. His son [her future husband] Other Archer Windsor 6th Earl Plymouth 1789-1833 (age 9) succeeded 6th Earl Plymouth, 12th Baron Windsor of Stanwell in Buckinghamshire.
On 19 Jul 1799 [her father] John Frederick Sackville 3rd Duke Dorset (age 54) died. His son [her brother] George Frederick Sackville 4th Duke Dorset 1793-1815 (age 5) succeeded 4th Duke Dorset, 10th Earl Dorset, 5th Earl Middlesex, 10th Baron Buckhurst, 5th Baron Cranfield of Cranfield in Middlesex.
In 1800 [her future husband] William Pitt Amherst 1st Earl Amherst (age 26) and [her future mother-in-law] Sarah Archer Countess Plymouth and Amherst (age 38) were married.
On 07 Apr 1801 [her step-father] (age 48) and [her mother] Arabella Diana Cope 3rd Duchess Dorset 1769-1825 (age 32) were married. She the daughter of Charles Cope 2nd Baronet and Catherine Bisshopp Countess Liverpool (age 56).
On 05 Aug 1811 Other Archer Windsor 6th Earl Plymouth 1789-1833 (age 22) and Mary Sackville Countess Plymouth Amherst (age 19) were married. She by marriage Countess Plymouth. She the daughter of John Frederick Sackville 3rd Duke Dorset and Arabella Diana Cope 3rd Duchess Dorset 1769-1825 (age 42). He the son of Other Windsor 5th Earl Plymouth 1751-1799 and Sarah Archer Countess Plymouth and Amherst (age 49).
Around 1817. Thomas Lawrence (age 47). Portrait of Mary Sackville Countess Plymouth Amherst (age 24).
In 1819 Robert Henry Herbert (age 29) and [her sister-in-law] Harriet Windsor (age 21) were married. She the daughter of Other Windsor 5th Earl Plymouth 1751-1799 and Sarah Archer Countess Plymouth and Amherst (age 57). He the son of Edward Clive 1st Earl Powis (age 64) and Henrietta Antonia Herbert 3rd Countess Powis (age 60). He a great x 4 grandson of King James II of England Scotland and Ireland. 
In 1825 [her mother] Arabella Diana Cope 3rd Duchess Dorset 1769-1825 (age 56) died.
In 1826 [her brother-in-law] Jeffrey Amherst (age 24) died.
In 1826 [her future husband] William Pitt Amherst 1st Earl Amherst (age 52) was created 1st Earl Amherst. [her mother-in-law] Sarah Archer Countess Plymouth and Amherst (age 64) by marriage Countess Amherst.
On 20 Jul 1833 [her husband] Other Archer Windsor 6th Earl Plymouth 1789-1833 (age 44) died aboard his yacht at Deptford, Kent [Map]. His uncle Andrew Windsor 7th Earl (age 69) succeeded 7th Earl Plymouth. Baron Windsor of Stanwell in Buckinghamshire abeyant between his daughters [her sister-in-law] Maria Windsor Marchioness Downshire 1790-1855 (age 43) and [her sister-in-law] Harriet Windsor (age 35).
In 1839 William Pitt Amherst 1st Earl Amherst (age 65) and Mary Sackville Countess Plymouth Amherst (age 46) were married. She by marriage Countess Amherst. She the daughter of John Frederick Sackville 3rd Duke Dorset and Arabella Diana Cope 3rd Duchess Dorset 1769-1825.
In 1842 John Hay-Williams 2nd Baronet (age 47) and [her former sister-in-law] Sarah Elizabeth Amherst (age 40) were married. She the daughter of William Pitt Amherst 1st Earl Amherst (age 68) and Sarah Archer Countess Plymouth and Amherst.
On 13 Mar 1857 [her husband] William Pitt Amherst 1st Earl Amherst (age 84) died at Knole House, Sevenoaks. His son [her former brother-in-law] William Amherst 2nd Earl Amherst 1805-1886 (age 51) succeeded 2nd Earl Amherst. Gertrude Percy Countess Amherst 1814-1890 (age 42) by marriage Countess Amherst.
On 20 Jul 1864 Mary Sackville Countess Plymouth Amherst (age 71) died.
Paternal Family Tree: Sackville
Maternal Family Tree: Catherine Bisshopp Countess Liverpool 1744-1827
Descendants Family Trees:
Kings Wessex: Great x 22 Grand Daughter of King Edmund "Ironside" I of England
Kings Gwynedd: Great x 19 Grand Daughter of Owain "Great" King Gwynedd 1100-1170
Kings Seisyllwg: Great x 25 Grand Daughter of Hywel "Dda aka Good" King Seisyllwg King Deheubarth
Kings Powys: Great x 20 Grand Daughter of Maredudd ap Bleddyn King Powys 1047-1132
Kings England: Great x 11 Grand Daughter of King Edward IV of England
Kings Scotland: Great x 18 Grand Daughter of William "Lion" I King Scotland
Kings Franks: Great x 18 Grand Daughter of Louis VII King Franks
Kings France: Great x 14 Grand Daughter of Philip "The Fair" IV King France
Great x 4 Grandfather: Edward Sackville 4th Earl Dorset
8 x Great Grand Son of King Edward III of England
Great x 3 Grandfather: Richard Sackville 5th Earl Dorset 9 x Great Grand Son of King Edward III of England
Great x 2 Grandfather: Charles Sackville 6th Earl Dorset 1st Earl Middlesex 10 x Great Grand Son of King Edward III of England
Great x 4 Grandfather: Lionel Cranfield 1st Earl Middlesex
Great x 3 Grandmother: Frances Cranfield Countess Dorset
Great x 1 Grandfather: Lionel Cranfield Sackville 1st Duke Dorset 10 x Great Grand Son of King Edward III of England
Great x 4 Grandfather: Spencer Compton 2nd Earl of Northampton
7 x Great Grand Son of King Edward III of England
Great x 3 Grandfather: James Compton 3rd Earl of Northampton 8 x Great Grand Son of King Edward III of England
Great x 4 Grandmother: Mary Beaumont Countess of Northampton 1604-1654
8 x Great Grand Daughter of King Edward III of England
Great x 2 Grandmother: Mary Compton Countess Dorset and Middlesex 1669-1691 9 x Great Grand Daughter of King Edward III of England
Great x 4 Grandfather: Baptist Noel 3rd Viscount Campden
Great x 3 Grandmother: Mary Noel Countess Northampton
Great x 4 Grandmother: Hester Wotton Viscountess Campden
GrandFather: John Sackville 11 x Great Grand Son of King Edward III of England
Great x 3 Grandfather: Alexander Colyear
Great x 2 Grandfather: Walter Colyear
Great x 1 Grandmother: Elizabeth Colyear Duchess Dorset 1689-1768
Father: John Frederick Sackville 3rd Duke Dorset 11 x Great Grand Son of King Edward III of England
Great x 4 Grandfather: Thomas Gower 2nd Baronet
Great x 3 Grandfather: William Leveson-Gower 4th Baronet
Great x 4 Grandmother: Frances Leveson Baroness Gower
Great x 2 Grandfather: John Leveson-Gower 1st Baron Gower
Great x 4 Grandfather: John Granville 1st Earl Bath
Great x 3 Grandmother: Jane Granville Baroness Gower
Great x 4 Grandmother: Jane Wyche
Great x 1 Grandfather: John Leveson-Gower 1st Earl Gower 10 x Great Grand Son of King Edward III of England
Great x 4 Grandfather: John Manners 8th Earl of Rutland
7 x Great Grand Son of King Edward III of England
Great x 3 Grandfather: John Manners 1st Duke Rutland 8 x Great Grand Son of King Edward III of England
Great x 4 Grandmother: Frances Montagu Countess Rutland
10 x Great Grand Daughter of King Edward "Longshanks" I of England
Great x 2 Grandmother: Catherine Manners Baroness Gower 9 x Great Grand Daughter of King Edward III of England
Great x 4 Grandfather: Baptist Noel 3rd Viscount Campden
Great x 3 Grandmother: Catherine Noel Duchess Rutland 11 x Great Grand Daughter of King Edward "Longshanks" I of England
Great x 4 Grandmother: Elizabeth Bertie Viscountess Campden
10 x Great Grand Daughter of King Edward "Longshanks" I of England
GrandMother: Frances Leveson-Gower 10 x Great Grand Daughter of King Edward III of England
Great x 4 Grandfather: William Pierrepont of Thoresby
8 x Great Grand Son of King Edward III of England
Great x 3 Grandfather: Robert Pierrepont 9 x Great Grand Son of King Edward III of England
Great x 4 Grandmother: Elizabeth Harries aka Harris
Great x 2 Grandfather: Evelyn Pierrepont 1st Duke Kingston upon Hull 10 x Great Grand Son of King Edward III of England
Great x 4 Grandfather: John Evelyn of Wiltshire
Great x 3 Grandmother: Elizabeth Evelyn
Great x 4 Grandmother: Elizabeth Coxe
Great x 1 Grandmother: Evelyn Pierrepont Baroness Gower 9 x Great Grand Daughter of King Edward III of England
Great x 4 Grandfather: George Feilding 1st Earl Desmond 1614-1665
Great x 3 Grandfather: William Feilding 2nd Earl Desmond 3rd Earl Denbigh 1640-1685 7 x Great Grand Son of King Edward III of England
Great x 4 Grandmother: Bridget Stanhope Countess Desmond 1615-1701
6 x Great Grand Daughter of King Edward III of England
Great x 2 Grandmother: Mary Fielding Countess Kingston upon Hull 1668-1697 8 x Great Grand Daughter of King Edward III of England
Great x 4 Grandfather: Henry Carey 2nd Earl Monmouth
7 x Great Grand Son of King Edward III of England
Great x 3 Grandmother: Mary Carey Countess Desmond and Denbigh 1632-1682 8 x Great Grand Daughter of King Edward III of England
Great x 4 Grandmother: Martha Cranfield Countess Monmouth 1601-
Mary Sackville Countess Plymouth Amherst 1792-1864 11 x Great Grand Daughter of King Edward IV of England
Great x 4 Grandfather: Johnathan Cope 11 x Great Grand Son of King Edward "Longshanks" I of England
Great x 3 Grandfather: Johnathan Cope 12 x Great Grand Son of King Edward "Longshanks" I of England
Great x 2 Grandfather: Johnathan Cope 1st Baronet 13 x Great Grand Son of King Edward "Longshanks" I of England
Great x 1 Grandfather: Johnathan Cope 14 x Great Grand Son of King Edward "Longshanks" I of England
Great x 4 Grandfather: Robert Jenkinson 1st Baronet
Great x 3 Grandfather: Robert Jenkinson 2nd Baronet
Great x 2 Grandmother: Mary Jenkinson Lady Cope
GrandFather: Charles Cope 2nd Baronet 9 x Great Grand Son of King Edward IV of England
Great x 4 Grandfather: Edward Howard 2nd Earl Carlisle
10 x Great Grand Son of King Edward III of England
Great x 3 Grandfather: Charles Howard 3rd Earl Carlisle 1669-1738 9 x Great Grand Son of King Edward III of England
Great x 2 Grandfather: Henry Howard 4th Earl Carlisle 10 x Great Grand Son of King Edward III of England
Great x 4 Grandfather: Arthur Capell 1st Earl Essex 9 x Great Grand Son of King Edward III of England
Great x 3 Grandmother: Anne Capell Countess Carlisle 9 x Great Grand Daughter of King Edward III of England
Great x 4 Grandmother: Elizabeth Percy Countess Essex 8 x Great Grand Daughter of King Edward III of England
Great x 1 Grandmother: Arabella Howard 8 x Great Grand Daughter of King Edward IV of England
Great x 4 Grandfather: Robert Spencer 2nd Earl of Sunderland
9 x Great Grand Son of King Edward III of England
Great x 3 Grandfather: Charles Spencer 3rd Earl of Sunderland 10 x Great Grand Son of King Edward III of England
Great x 4 Grandmother: Anne Digby Countess Sunderland
9 x Great Grand Daughter of King Edward III of England
Great x 2 Grandmother: Frances Spencer Countess Carlisle 1696-1742 7 x Great Grand Daughter of King Edward IV of England
Great x 4 Grandfather: Henry Cavendish 2nd Duke Newcastle upon Tyne
5 x Great Grand Son of King Edward IV of England
Great x 3 Grandmother: Arabella Cavendish 6 x Great Grand Daughter of King Edward IV of England
Great x 4 Grandmother: Frances Pierrepont Duchess Newcastle upon Tyne 1630-1695 9 x Great Grand Daughter of King Edward III of England
Mother: Arabella Diana Cope 3rd Duchess Dorset 1769-1825 10 x Great Grand Daughter of King Edward IV of England
Great x 4 Grandfather: Edward Bisshopp 2nd Baronet 9 x Great Grand Son of King Edward III of England
Great x 3 Grandfather: Cecil Bisshopp 4th Baronet 9 x Great Grand Son of King Edward III of England
Great x 4 Grandmother: Mary Tufton 8 x Great Grand Daughter of King Edward III of England
Great x 2 Grandfather: Cecil Bisshopp 5th Baronet 10 x Great Grand Son of King Edward III of England
Great x 1 Grandfather: Cecil Bisshopp 6th Baronet 11 x Great Grand Son of King Edward III of England
GrandMother: Catherine Bisshopp Countess Liverpool 12 x Great Grand Daughter of King Edward III of England