(Histories written in the mid- 19th century from early Latin records are often contradictory, therefore no guarantee of the accuracy of the following names and dates can be assured, although every effort has been made to confirm them using the original and other sources.)
Ranulfe de Ducey (Latin: Ranulfum de Dusseio) – probably not the first, but the first known, of the seigneurs of the Ducey fief, circa 1095 – 1140. Historian Jean-Jacques Desroches said s he was listed on a charter at the Abbey of Savigny in 1095 but this is yet to be found on a list of the Savigny charters. However Ranulfe is recorded as present at the Council of Rouen, held 07 October 1118.
His son, Robert (1) (Lt.: Roberti de Duxxeio) – as was the custom of the times, made an important pledge to the Abbey Mont Saint-Michel in the presence of Ranulfe. With Robert was his wife Cecile and young son William(1). They later had a 2nd son, Robert(2) and a daughter Mathilde(1)  However some historians confuse her with the more prominent Mathilde de Ducey, the daughter of Robert(2) and thus the niece of William (1). Regrettably, historians differ over the exact year of Robert (1)’s charter at Mont Saint-Michel, citing dates of 1118, 1128, 1120-30 and as late as 1135. From my readings of the available research, I believe it to be 1128 AD.
The elder Robert(1), son of Ranulfe, has died. 
sons of Robert de Ducey-
– There is little further word of son Robert (2).
– William de Ducey (1) . born c. 1117 -He is said to have been schooled at the Abbey of Mont Saint-Michel. He marries Marie, rich by her own inheritances. He was described as an illustrious benefactor to several parishes in the Avranches area. He is recorded as one of the founders of the abbey at Montmorel. Most histories say he was only seigneur from 1171-1180, however see note just below.
1140 William (1), with the approval of wife Marie, pledges the patronage of the churches of Champcervon and St. Martin-le Bouillant to the abbey of Savigny.
1180 William (1) dies at Ducey, attended by the Bishop of Avranches. He is buried at Savigny.
dtr. of Robert (2)
Mathilde(2) She inherits the Ducey fief and is the last known family member of the Robert de Ducey branch. She will later marry William de Husson(1), said to succeed her late brother as seigneur of Ducey from 1180 until his death in 1195.
However this conflicts with the dates of Hervé and Hugh (below) but suggests the possibility there could be more than one seigneur at the same time from the same fiefdom, which contained several parishes. (There could also be two seigneurs de Ducey while both father and son are alive, as was probably the case with Ranulfe and Robert (1).
sons of William(1)? There is very little historical evidence of any offspring, but:
b. 1147 Hervé de Ducey -believed to be the first son of William (1), is said to become seigneur of Ducey in 1180. His reign ends in 1220.
Ernaldus – second son.
dtrs. of William? Aeliz and Giseleberthe
These four are recorded as on the Tax Rolls of Normandy in 1198.
1190? Mathilde (2), daughter of Robert(2) and thus niece of the illustrious William de Ducey (1), having married William de Husson (1), has a son, Foulques de Husson.
William Husson dies. Mathilde later marries Nigel, Count of Mortain and will outlive him too.
1227-28 Another William de Husson (2), seigneur of Ducey, is recorded at Avranches as making a charter of confirmation to the abbey of Savigny.
1180 – 1250 Hugh de Ducey – Also said to be a seigneur of Ducey.
1224 Hugh de Ducey is called upon by King Phillip II to serve on a jury with fellow knights judging a high-level property dispute, held at Caen. He is said to have had two sons.
sons of Hugh de Ducey
1272 – William de Ducey (2 or 3 ?) – c. 1215 – 1275 said to be a seigneur of Ducey. He is believed to be the knight, William de Ducey, who pledged support to King Phillip III at Tours in 1272.
John de Ducey – c. 1280 – 1335 (“domino Johanne de Duxyeo”) Inherits the fief of Ducy-Ste. Marguerite.
1270 Foulques de Husson marries and has a son, Fraslin de Husson.
1302 Foulques dies and his son, Frasalin de Husson becomes seigneur of Ducey as the Ducey family ends its tenure of the Ducey fief.
1326 “Sir ——- Ducey,” according to English historians, a French knight, among several others, raises a regiment in support of Queen Isabella of England and Sir Roger Mortimer . A fleet of at least eight warships sail from Normandy to Holland and then to England. This army of mercenaries is led by John of Hainault and the invaders successfully depose her husband, Edward II.
For this service,” Sir ——- de Ducey” is awarded lands in Staffordshire. One source believes he sold his lands in Normandy to his neighbor, Fulco de Husson. 
1346 — The town of Ducey, its chateau, church and surrounding area, is razed to the ground by English forces led by Renaud de Gobehen, under the flag of King Edward III. 
1415 Olivery de Ducey, believed to be a descendant of John de Ducey, is slain by the forces of King Henry V of England at the battle of Agincourt. His lands at Ducy Ste. Marguerite are later seized by royal decree. 
1420 – 1521 After peace is finally restored between England and France, the Ducey fief passes down through the families of Husson, Laval, Pontbriend, and de la Boissiere.
1521 Through a marriage of Claude La Boissiere and Jacques Montgommery, the fief of Ducey will pass into the Montgommery family, the French branch of an ancient Scottish clan active in France for several centuries. They will be seigneurs of the Ducey fief until 1711.
1789. The manorial (fiefdom) system is abolished in France during the reforms of 1789.
 C.H. Hoskins, Norman Institutions, (Law Book Exchange, Clark, N.J., 2007), p.294.
 Jean Jacques Desroches, Annales Civils et Militaires du Pays d’Avranches, ou de la toute Basse-Normandie. (Caen: A. Hardel, 1856), 62, 138-9. Also, La Manche – Part 1, British History Online, Charter of Robert de Duxeio, no210, fo. 85d , period 1120 -1130 AD.
 Ibid, Desroches, 139.
 Ibid, 39, 150.
 Ibid. 139. Also: Ed. Memoires de la Societe Academique du Cotentin, tome septieme, (Avranches, Alfred Perrin 1891), 704-05. (In 1227 the Hussons confirmed the donation in 1140 by William de Ducey, giving the support of the church at St. Martin-le-Bouillant to the Abbey of Savigny.)
 Loc cit., 151.
 Ibid, 152, 156.
 Sister Agnes Ducey, The Ducey Story (Omaha, Nebraska: 1966), 7. Also Valérie Houlbert, Ducey, a la recherché de son passé (Ducey, Office de Tourisme de Ducey, 2007}, 10.
 Loc. cit. p. 156.
 Ibid. p. 249.
 Sister Agnes Ducey. p. 14.
 Desroches, pp. 258-259.
 Sister Agnes Ducey, p. 19.
 Loc. cit. p. 259.
 E. Brydges, Collins Peerage of England, Vol. VII, (London, et.al. 1812), 410.
 Sister Agnes Ducey, p. 26. Her assumption that this knight was “William”and sold his property is not supported– it is theory .
 Desroches, p. 312.
 www.Battle of Agincourt, on an English list of “frenchmen slain in battle,” ‘Le Sire de Ducey.’