The chronology of the Vikings in Normandy can be encapsulated by a division into two successive centuries:

From AD 820 to c. AD 920, the Viking incursions on the lower Seine became more and more frequent, resulting finally in some permanent colonisation.
From c. AD 920 to AD 1020 was a consolidation period for Normandy, with the influx of numerous Scandinavian settlers, before turning increasingly to the Kingdom of France.

Timeline showing the Viking raids on the river Seine

820 Thirteen ships reach the Seine Bay. A force of Vikings lands but, having to face the shore guard, they are forced to re-embark, leaving five of their number dead on the Neustrian shore.
841 Asgeir’s fleet sails up the River Seine (from 12th May), takes the city of Rouen (14th May) and burns it down. The loot is enormous. Aesgir’s army continues its penetration of the Seine, plunders and burns the rich Jumiège monastery (24th May). The nearby monastery of Fontenelle (the future Saint-Wandrille) is also assaulted and held to ransom. In this expedition, sixty-eight captives are taken and then returned on payment of a ransom by the monks of Saint-Denis (28th May).
845 Ragnar’s fleet of 120 ships (therefore c. 6000 men) sails up the Seine and besieges Paris (28th March). Charles the Bald pays 7000 livres in order to spare Paris.
851 Asgeir and his men, back on the Seine, this time devastate the monastery of Fontenelle (13th October) and return there eighty-nine days later (9th January 852) and, finding nothing to plunder, burn it down.
852 Asgeir and his force raid on foot in the Beauvais region (Flanders county), from their base in Rouen. Engaged by a Frankish army, they have to withdraw and camp for the winter on Jeufosse island, securely controlling the entrance to the Seine. They stay there up to the 5th June. By the end of this year, a new group of Vikings, mainly Norwegians led by Sigtrygg (back from Ireland) and Godfrid, sails up the Seine to Jeufosse to establish their own base there. The Frankish army of Charles the Bald besieges the island.
853 (beg.) Charles the Bald negotiates with Godfrid, who afterwards retires. As for Sigtrygg, he stays to plunder and burn numerous places up to March.
855 Sigtrygg returns (18th July) to attempt to destroy a Frankish fort located on the Seine shore on the approach to Paris. He is reinforced by Björn, leading a powerful fleet (17th August). The two armies join and carry out a raid in the south of the Seine, as far as Chartres, where they are stopped by the Frankish army of Charles the Bald. They have to withdraw to the Seine after heavy losses.
857 Again from Jeufosse, which has now become an established base, Sigtrygg’s and Björn’s armies attack Paris (January). Chartres is assaulted again (12th June); on this occasion, revenging the reverse of AD 855, they take it, plunder it, and slaughter all its population. During the summer they also attack Evreux and many other places, the action taking place generally around Jeufosse island. Finally, Sigtrygg retires with his men.
858 Björn is joined by a new group of Danes, led by Hasting (9th January). They lay again into the abbey of Fontenelle, which they burn down. Leading a mounted force, Björn surrounds Paris and demands a ransom of the Parisian monasteries. Charles the Bald is defeated when he reacts and tries again to besiege the Viking base of Jeufosse.
859 The attacks from the Seine valley are redoubled. Charles the Bald is engaged in a struggle with his brother, Louis the German. The Vikings take advantage of this to attack freely far from their bases: Bayeux, Laon and Beauvais, where the bishops are executed.
860 The Viking chief, Veland, is paid 3000 silver livres by Charles the Bald to try to drive out the Vikings of the lower Seine.
861 From May, Veland besieges Jeufosse island, leading 200 Viking ships. The Vikings of Jeufosse have to retire from the Seine, with some 100 ships. This fleet then joins Veland’s. Taking advantage of several years of respite, Charles the Bald builds forts which control the Seine at Pont-de-l’Arche.
865 Fifty Viking ships settle at Pîtres (near Pont-de-l’Arche), on the Seine.
876 100 new Viking ships make an incursion into the Seine. They sail away again after a payment of 5000 livres by Charles the Bald.
885 A huge fleet sails up the Seine (one report tells of some 700 ships) to besiege Paris. Losses are severe on both sides. The new Frankish king, Charles the Big, relieves the city by paying a heavy ransom to the besiegers.
887-911 Rolf (Rollo/Rollon) imposes himself as chief of the Vikings settled in the lower Seine region. He repels the Franks, pushing right up to the doors of the Ile-de-France. He attacks Chartres but, repulsed, withdraws again to the Seine.
911 Seeking to block the lower Seine, which had become a real “motorway” for the Viking invasions of the Kingdom of Frankia, the new king, Charles the Simple, concludes an agreement with Rolf at Saint-Clair-sur-Epte, conceding to him the suzerainty of the territory of the lower Seine which, de facto, Rolf had already had for several years.

Timeline showing the Viking Raids in Western Neustria

From AD 836 Björn and Hasting lead numerous raids in Cotentin and Avranchin.
860-989 There are no more resident bishops in Cotentin and Avranchin nor any ecclesiastical infrastructures in these bishoprics. Whole areas are deserted by the native population as they become untenable, particularly in Cotentin.
867 The Frankish king, Charles the Bald, concedes Cotentin and Avranchin to the Bretons, so that they might defend these territories.
889, 890 and 891 Respectively, Saint-Lô, Coutances and Avranches are plundered or burnt down.
890-892 Rolf makes several raids in Bessin (Bayeux).
905 Vire is plundered.
907 Since Brittany is too devastated by the Viking raids, the Breton sovereignty of Cotentin and Avranchin exists only theoretically.
911 Since Rolf is now Jarl of Rouen, and since they refuse to convert to Christianity, and seek new conquests, many of Rolf’s companions settle in Cotentin and Bessin.
916 From Cotentin and Bessin, where they have settled, numerous Scandinavian forces attack the whole eastern region of Brittany.
924 Bessin is added to Rolf’s territory.
925 Some unsubdued Scandinavian troops of Bessin, united with native Saxons, devastate the western part of the Seine colony.
927-928 Rolf erect many fortifications (Bayeux, Exmes, Saint-Lô, Brionne, etc.) to face a huge influx of new Viking contingents, resistant to his authority in Cotentin (Danes from the Danelaw, and Hiberno-Norse from Ireland) and in Bessin (especially Danes from the Danelaw).
931 Brittany is totally subdued: on the east by the Normans of the Seine and on the west by Normans who have settled on the River Loire. The Normans of the Seine take advantage of this to get a foothold in Cotentin and Avranchin, and on the Channel Islands, in order to control the Scandinavian troops which have to submit to the Jarl of Rouen’s authority.
933 Cotentin and Avranchin are conceded officially by the King of France, Raoul, to the Normans of the Seine, who are also appointed to the protectorate of Brittany.