Montmagny-L'Islet () is a former provincial electoral district in the Chaudière-Appalaches region of Quebec, Canada that elected members to the National Assembly of Quebec. As of its final election, it included the cities or municipalities of Montmagny, Saint-Jean-Port-Joli, L'Islet, Sainte-Perpétue, Saint-Pamphile and Cap-Saint-Ignace.
It was created for the 1973 election from Montmagny and a part of L'Islet. Its final election was in 2008. It disappeared in the 2012 election and the successor electoral district was Côte-du-Sud.
Its territory never changed during its entire existence, despite overall electoral map reforms in 1980, 1985, 1988, 1992 and 2001.
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|Liberal |Norbert Morin |align="right"|10,027 |align="right"|51.78 |align="right"|+13.59
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|Liberal |Norbert Morin |align="right"|8,829 |align="right"|38.19 |align="right"|-2.98
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<nowiki>*</nowiki> Increase is from UFP
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|Liberal |Norbert Morin |align="right"|9,518 |align="right"|41.17 |align="right"|-4.82
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|Liberal |Réal Gauvin |align="right"|11,047 |align="right"|45.99 |align="right"|+1.63
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|Liberal |Réal Gauvin |align="right"|10,339 |align="right"|44.36 |align="right"|-13.39
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|Independent |Jean-Claude Roy |align="right"|2,605 |align="right"|11.18 |align="right"|- |-
|New Democrat |Gaston Bourget |align="right"|881 |align="right"|3.78 |align="right"|-
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|Liberal |Réal Gauvin |align="right"|12,688 |align="right"|57.75 |align="right"|-2.77
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|Liberal |Réal Gauvin |align="right"|14,492 |align="right"|60.52 |align="right"|+15.92
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|New Democrat |Louise Saint-Pierre |align="right"|564 |align="right"|2.35 |align="right"|- |-
|Independent |Antonio Cicchetti |align="right"|500 |align="right"|2.09 |align="right"|- |-
|Parti indépendantiste |Alain Raby |align="right"|199 |align="right"|0.83 |align="right"|- |-
|Christian socialist |Réjean Tardif |align="right"|47 |align="right"|0.20 |align="right"|-
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|Liberal |Julien Giasson |align="right"|11,566 |align="right"|44.60 |align="right"|+7.16 |-
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|Liberal |Julien Giasson |align="right"|9,220 |align="right"|37.44 |align="right"|-14.44 |-
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|Liberal |Julien Giasson |align="right"|11,375 |align="right"|51.88 |-
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|Parti créditiste |Yvon-C. Roy |align="right"|2,227 |align="right"|10.16