Indeed there is: the North German plain is Low Germany: see this from Wikipedia

Variants of Low German were widely (and are still to a far lesser extent) spoken in most parts of Northern Germany, for instance in the states of Lower Saxony, North Rhine-Westphalia, Hamburg, Bremen, Schleswig-Holstein, Mecklenburg-Vorpommern, Saxony-Anhalt and Brandenburg. Small portions of northern Hesse and northern Thuringia are traditionally Low Saxon speaking too. Historically, Low German was also spoken in formerly German parts of Poland as well as in East Prussia and the Baltic States of Estonia and Latvia. The language was also formerly spoken in the outer areas of what is now the city state of Berlin but in the course of urbanisation and national centralisation in that city the language vanished.