Fun fact to kick things off: St. Ogg’s and Dorlcote Mill are actually based on Eliot’s own childhood home in Warwickshire, England. Warwickshire is a county located in the middle of England, or the "Midlands."
Though published in 1860, The Mill on the Floss is set about forty years prior, around the 1820s. We never get an actual date in this book, but a couple of historical references have led scholars and critics to place it around the 1820s. For instance, we learn that Mr. Poulter fought in the "Peninsular War," which was a conflict involving Napoleon. Tom’s encounters with Mr. Poulter would have taken place sometime after Napoleon was defeated, so after 1815 basically. There are also references to political figures, like the Duke of Wellington, and political issues that place the novel around the 1820s.
So, we’ve got time period out of the way. It’s important to note that this novel is set in the Midlands and takes place largely at an industrial mill. The Midlands were the major site for England’s Industrial Revolution. This gives us some insight into our characters. Lots of the people living in the Midlands in this period made their living in some sort of business profession. In other words, these people weren’t all just farmers, and the wealthy people in the novel (like the Deanes) made their money through business as opposed to inheritance. Business, industry, and legal procedures were a growing part of this society. And business and the law often made this society very precarious, or unstable. As we see through Mr. Tulliver’s disastrous lawsuit, people could lose everything (home, money, possessions) very quickly. Reputations were also lost quickly in a small community that had very strict Victorian social codes, which were even stricter for women.
This was very much a world in transition, as we can see through Tom’s education. Tom gets a very old-fashioned "gentleman’s" education, which doesn’t help him in the modern business world. Tom’s education helps to shed light on the importance of class in this world too. Tom, who has to work for a living, definitely requires a different sort of education than someone like Philip Wakem or Stephen Guest, who are wealthy enough to not worry about learning a trade and getting actual job skills. Their respective fathers have been so successful at business that Stephen and Philip don’t really have to work now.
Narrowing things down further, we come to the town of St. Ogg’s and Dorlcote Mill itself. As the narrator points out, this is a very narrow world. We rarely stray very far from these two places. But, while this world is small, it isn’t entirely clausterphobic. The river and business bring in things from the wider world, be it the "Swedish bark" Mr. Deane discusses with Tom (3.5.53) or the Dutch trading ship that picks up Maggie and Stephen (6.13.55). However, the characters themselves rarely stray far from home and they interact almost exclusively with other family members. This is a tightly-knit community for better or worse. And it’s often for worse: St. Ogg’s is a town ruled by gossip and rumors and prejudices, as Maggie Tulliver finds out the hard way.
This sense of isolation and narrowness is reinforced early on in the novel. Here’s the narrator’s first take on this sense of isolation, which isn’t necessarily a bad thing:
The rush of the water and the booming of the mill bring a dreamy deafness which seems to heighten the peacefulness of the scene. They are like a great curtain of sound, shutting one out from the world beyond. (1.1.3)
The narrator emphasizes from the start that the world in which this novel takes place is isolated and somewhat removed from the "world beyond." But this world is also dynamic and surprisingly complex, as the description of energetic sounds reveal. And, above all else, this tiny world is one of contrasts: it is both modern and dynamic, filled with "booming" mills, yet old-fashioned and even "dreamy."