The Mill on the Floss takes place in St. Ogg’s, a fictional town in Lincolnshire, England. Lincolnshire is in the Midlands of England (or, the middle of the country), a key site of the Industrial Revolution. This location explains the importance of Dorlcote Mill (the Tulliver family mill) as an industrial mill that brings in money for the Tulliver family (and has for several generations). This location also explains why there are no aristocratic people in the novel who have inherited wealth—in the Midlands at this period in time, most people were involved in industry and commerce.
The novel is set in the 1820s, in the period following England’s triumph in the Napoleonic wars. This is apparent in several moments, such as when characters reference how Mr. Poulter fought in the “Penninsular War.” In the aftermath of the war, many Englanders were proud of their country and had a renewed faith in the British Empire.
Throughout the novel, different characters reference “the Catholic Question,” an allusion to the Catholic Relief Act of 1829 (which, at the time the book is set, was merely a bill being debated). This was a piece of legislation that finally allowed Catholics to become Members of Parliament, a change that the conservative, small-town St. Ogg’s townspeople generally don’t support. As someone involved with the progressive politics of her time, Eliot was likely trying to expose the prejudice and ignorance that provincial townspeople in England have sometimes perpetuated via her characters criticizing the bill.
It is worth noting that many scholars view The Mill on the Floss as Eliot’s most autobiographical novel, as her relationship to her brother Isaac mirrors Maggie’s relationship with Tom in many ways. As such, it’s possible that St. Ogg’s is based on Eliot’s hometown in Warwickshire. It’s also possible that Eliot’s decision to center a bookish woman who diverted from female social norms in England in the 19th century was her way of processing her own challenges as a woman writer at this time.
