Work on the Closing Dam ('Afsluitdijk') was started in 1927 and it was finished in 1932.
The reclaimed land:
Andijk was a small 1927 experiment.
Wieringermeer (1927-30) 190 km², 75 sq. miles
Noordoostpolder (1937-42) 465 km², 180 sq. miles
Oostelijk Flevoland (1950-57) 525 km², 200 sq. miles
Zuidelijk Flevoland (1959-68) 425 km² 165 sq. miles
For the Markerwaard (400 km² 155 sq. miles) some dams were laid, but its completion is postponed indefinitely.

Maps Overview - 300 AD CE - 1000 AD CE - 1650 AD CE - 1900 AD CE - at present*

Low and High Ground - 20th Century Land Reclamation - The Delta Protection Works*
* - with names spoken

Old and New
Zuiderzee
Urk
Schokland
Afsluitdijk ("Closing Dam")
IJsselmeer
hear (ca 50K)

Urk and Schokland were islands in the old Zuyder Zee.

The Reclaimed Land
Andijk
Wieringermeer
Noordoostpolder
hear (ca 50K)

Oostelijk Flevoland
Zuidelijk Flevoland
Markerwaard
hear (ca 50K)

Cities Old
Hindeloopen
Stavoren
Lemmer
hear (ca 50K)

Urk - see (hear) 'Old and New' above

Kampen
Harderwijk
Amsterdam
hear (ca 50K)

Volendam
Hoorn
Enkhuizen
Medemblik
hear (ca 50K)

Cities New
Wieringerwerf
Emmeloord
Dronten
hear (ca 50K)

Lelystad
Almere
Zeewolde
hear (ca 50K)