Exodus 7:21: And the fish that were in the river died; and the river became foul, and the Egyptians could not drink water from the river; and the blood was throughout ALL the land of Egypt.
Exodus 8:13: ...and Aaron stretched out his hand with his rod, and smote the dust of the earth, and there were gnats upon man, and upon beast; all the dust of the earth became gnats throughout ALL the land of Egypt.
Exodus 8:20: ...and in ALL the land of Egypt the land was ruined by reason of the swarms of flies.
Exodus 9:6: And the LORD did that thing on the morrow, and ALL the cattle of Egypt died; but of the cattle of the children of Israel died not one.
Exodus 9:6: And it shall become small dust over all the land of Egypt, and shall be a boil breaking forth with blains upon man and upon beast, throughout ALL the land of Egypt.
Exodus 9:25: And the hail smote throughout ALL the land of Egypt all that was in the field, both man and beast; and the hail smote every herb of the field, and broke every tree of the field.
Exodus 10:14: And the locusts went up over ALL the land of Egypt, and rested in ALL the borders of Egypt
Exodus 10:22: And Moses stretched forth his hand toward heaven; and there was a thick darkness in ALL the land of Egypt three days
Exodus 12:29: And it came to pass at midnight, that the LORD smote ALL the firstborn in the land of Egypt
Let's consider the geography of Egypt. Goshen is in the the northeast section of Egypt. All of the Jews are concentrated there. The central government of the 19th Dynasty (roughly contemporaneous with the Exodus story) is in Avaris & Pi-Ramesse just to the east of Goshen. Close by is another major population center, Tanis, and a bit farther are the cities of Heliopolis and Giza (site of the Great Pyramid & the Sphinx.) As one travels south into Upper Egypt, major population centers include Memphis (home to Elvis), Amarna, Abydos, and Elephantine, and finally Abu Simbel, located more than 600 km from Pi-Ramesse (upstream) via the Nile, or about 500 km as the crow flies. Some maximum traveling comparison times estimated by Eerdman's Dictionary of the Bible: armies 24 km/day; foot journey - 32 km/day; horseback 40-50 km/day; chariot 72 km/day; couriers 95 km/day.
Now it is easy to justify a massive conflagration against the people in Lower Egypt, since the oppression of the Jewish people would have required the cooperation of a multitude of Egyptians there. But does anyone really believe that the population centers of the more southern cities had any clue as to what was going on in the north? They likely had no clue as to the situation with the Jews in Goshen, and certainly had no part in their subjugation. It was a long and arduous journey to the north and they probably had only sporadic news reports about the construction of various government projects. Of course it was taken for granted that a slave labor force would be employed, that was typical in the Ancient Near East . (Myth quashing digression: the great pyramids were built 1000 years earlier in the 4th Dynasty, approximately 2500 BCE, and slave labor was NOT used.) Let's face it, most of the population consisted of poor farmers eking out a living. There is no way that they could have been complicit in the brutality towards the Jews of Goshen, yet God punishes them as harshly as the northerners!
Note in particular the "advanced warning" that Moses gives the Egyptians in the plague of hail. Exodus 9:18 ff: "Behold, tomorrow about this time I will cause it to rain a very grievous hail, such as hath not been in Egypt since the day it was founded even until now. Now therefore send, hasten in thy cattle and all that thou hast in the field; for every man and beast that shall be found in the field, and shall not be brought home, the hail shall come down upon them, and they shall die.' He that feared the word of the LORD among the servants of Pharaoh made his servants and his cattle flee into the houses; and he that regarded not the word of the LORD left his servants and his cattle in the field." It's obvious that only those able to take heed of the warning were so forewarned (the servants of Pharaoh). There is no suggestion that all of the people of Egypt were warned, and yet the hail devastated ALL of Egypt!
Of course, this would not be first nor last time that God was the architect of a disproportionate response according to a literal reading of the Torah. But, just as the annihilation of the Canaanite people never really occurred, I would like to think that these plagues were very localized and did not affect the entire land of Egypt as the Torah states. (Even a naturalistic explanation of the plagues - which I am quite fond of - would suggest this.) What we have here is hyperbole, folks, and the Torah is chock full of this literary technique. Get used to it.