John died between 1768 and 1779 if his wife Margaret a widower remarried.  There is no burial record at Hawarden, but there is for John in 1797 of expected age, so widower Margaret may have been another.

Name    John Millington
Age    67
Birth Year (Estimated)    1730
Event Type    Burial
Event Date    26 Jan 1797
Event Place    Hawarden, Flintshire, Wales
Page    64

There is a burial record for John Millington at Chester Holy Trinity, 18th May
    
Cheshire Diocese Of Chester Bishop's Transcripts Burials 1576-1906
Church:
Holy Trinity, Cheshire, England
Year 1778
Age and parents not given (so probably an adult)

Name:    Margareta Youde
Baptism Age:    0
Record Type:    Baptism
Birth Date:    1728
Baptism Date:    12 Feb 1728
Baptism Place:    Hawarden, Flintshire, Wales
Father:    Johis
Page number:    9

Abode: Mancott

Name(s) Margaret Adams
Spouse's residence , Shotwick
Gender Female
County Cheshire
Age -
Country England
Birth year -
Reference p 31
Death year -
Record group Part 1 - 74
Burial year 1786
Record set Cheshire Diocese Of Chester Parish Burials 1538-1911
Burial date 08 Jan 1786
Category Birth, Marriage, Death & Parish Records
Place Shotwick
Subcategory Parish Burials
Residence Shotwick
Collections from England, Great Britain
Spouse's first name(s) Thomas

Name:    John Millington
Baptism Age:    0
Record Type:    Baptism
Birth Date:    1750
Baptism Date:    6 Feb 1750
Baptism Place:    Hawarden, Flintshire, Wales
Father:    John
Page number:    66

John son of John Millington of Harden (i.e. Hawarden)
John of Shotton when married

Name    John Millington
Death Age    60
Record Type    Burial
Birth Date    1748
Death Date    abt 1808
Burial Date    15 May 1808
Burial Place    Hawarden, Flintshire, Wales
Page number    8

John Millington, Collier of Ewloe, Aged 60

Name:    Mary Millington
Baptism Age:    0
Record Type:    Baptism
Birth Date:    1752
Baptism Date:    4 Dec 1752
Baptism Place:    Hawarden, Flintshire, Wales
Father:    John
Page number:    70

Mary, daughter of John Millington, Hawarden

Name:    Mary Millington
Record Type:    Burial
Death Date:    abt 1753
Burial Date:    3 May 1753
Burial Place:    Northop, Flintshire, Wales
Page number:    9

Abode: Northop.  No ages gives on these records

Mary Millington
Wales, Flintshire, Parish Registers, 1538-1912

Name:    Mary Millington
Event Type:    Baptism
Event Date:    23 Feb 1755
Event Place:    Hawarden, Flintshire, Wales

Mary, daughter of John and Margaret Millington of Hawarden

Mary must have died before 1770, as another Mary of Hawarden was baptised then.

She was born in Hawarden and probably died there or close by. 

Name:    Mary Millington
Event Type:    Burial
Event Date:    30 Apr 1763
Event Place:    Connah's Quay, Flintshire, Wales

Burial in 1820, aged 63, so born about 1757


Name:    Thomas Millington
Baptism Age:    0
Record Type:    Baptism
Birth Date:    1757
Baptism Date:    26 Jun 1757
Baptism Place:    Hawarden, Flintshire, Wales
Father:    J
Mother:    Margaret
Page number:    94

Tho's S: of J & Marg't Millington . Haward'n

Thomas Millington - Wales, Flintshire, Parish Registers, 1538-1912
Name:    Thomas Millington
Event Type:    Baptism
Event Date:    01 May 1753
Event Place:    Northop, Flintshire, Wales

There are other Thomas Millingtons:
June 1757: Tho's S of Geo & Mary Millington of Pentrobin

Death: 25 July 1820
Hope Owen, Flintshire, Wales

Thomas Millington - Wales, Flintshire, Parish Registers, 1538-1912
Name:    Thomas Millington
Event Type:    Burial
Event Date:    25 Jul 1820
Event Place:    Hawarden, Flintshire, Wales
Age:    63
Birth Year (Estimated):    1757

Abode: Hope, Collier

Name:    Margaret Millington
Baptism Age:    0
Record Type:    Baptism
Birth Date:    1760
Baptism Date:    14 Sep 1760
Baptism Place:    Hawarden, Flintshire, Wales
Father:    John
Mother:    Margaret
Page number:    7

Marg't D: of Jn'o & Marg't Millington of Shotton

Name:    Margaret Jones
Death Age:    34
Record Type:    Burial
Birth Date:    1760
Death Date:    abt 1794
Burial Date:    4 May 1794
Burial Place:    Hawarden, Flintshire, Wales
Spouse:    Joseph
Page number:    59

Margaret, wife of Joseph Jones a fisherman of Shotton, aged 34

Pedigree Resource File:

Birth: 25 December 1764
Mancot, Flintshire, Wales

Mancott is next to Queensferry, Deeside and about 1 mile SE of Shotton

Name:    Rachel Millington
Baptism Age:    0
Record Type:    Baptism
Birth Date:    1763
Baptism Date:    23 Jan 1763
Baptism Place:    Hawarden, Flintshire, Wales
Father:    John
Mother:    Margaret

Rachel D'r of Jn'o & Marg't Millington of Shotton

Name    Rachel Davies
Death Age    73
Record Type    Burial
Birth Date    1764
Death Date    abt 1837
Burial Date    10 Apr 1837
Burial Place    Hawarden, Flintshire, Wales
Spouse    Edward
Page number    252

Rachel widow of Edward Davies, collier, of Pentrobin, died aged 76

Aged 83 or 84 when died, so born about 1761 - 1862

Name:    Elizabeth Millington
Baptism Age:    0
Record Type:    Baptism
Birth Date:    1765
Baptism Date:    24 Mar 1765
Baptism Place:    Hawarden, Flintshire, Wales
Father:    John
Mother:    Margaret
Page number:    24
Pentrobin, Shotton, Wales, United Kingdom

NOTE: The Millennium File has mother as Susannah Bannion.  However that is another John Millington family from Pentrobin, Hawarden.  This is Elizabeth Millington of Shotton, daughter of John and Margaret baptised at Hawarden 24 Mar 1765 (same date).  There is no other Elizabeth Millington baptised at Hawarden so Millenniums File must be in error.

Millenium File:
Name    Elizabeth Millington
Gender    Female
Birth Date    24 Mar 1764
Birth Place    Hawarden, Flints, Wales
Death Date    1845
Father    John Millington
Mother    Susannah Bannion
Spouse    Benjamin Bennett
Children    Benjamin Bennett

Death: November 1845
Holywell, Flintshire, Wales, United Kingdom

Its more likely Elizabeth died in Golftyn near Connah's Quay or Wepre, and the death was registered at Holywell

BENNETT, ELIZABETH        84 
GRO Reference: 1845  S Quarter in HOLYWELL 
Volume 27  Page 147

North Wales Death indexes for the years: 1845
BENNETT    Elizabeth    -    Flint    Flintshire (Mold)    FLNT/03/84

Name:    Elizabeth Bennett
Death Age:    83
Record Type:    Burial
Birth Date:    1762
Death Date:    abt 1845
Burial Date:    15 Jul 1845
Burial Place:    Northop, Flintshire, Wales
Spouse:        Benjamin
Page number:    30
"Elizabeth, widow of Benjamin Bennett (Fisherman)" of Wepre Township was buried July 15th 1845, aged 83.

Name:    Ann Millington
Baptism Age:    0
Record Type:    Baptism
Birth Date:    1768
Baptism Date:    10 Jun 1768
Baptism Place:    Hawarden, Flintshire, Wales
Father:    John
Mother:    Mary  (should be Marg't)
Page number:    36

Baptism records shows daughter of Jn'o & Margaret of Shotton

Name:    Ann Williams
Event Type:    Burial
Event Date:    24 Apr 1847
Event Place:    Bagillt, Flintshire, Wales
Age:    75
Birth Year (Estimated):    1772

Name    Ann Williams
Death Age    43
Record Type    Burial
Birth Date    1767
Death Date    abt 1810
Burial Date    29 Jun 1810
Burial Place    Hawarden, Flintshire, Wales

Ann, wife of Samuel Williams, Labourer