The graphic provided at the bottom of this page is a cheat sheet for addressing unmarried ladies, be they the daughters of aristocrats, gentry, or otherwise. Addressing unmarried women of commoner status is straight forward, but the daughters of aristocratic lineage can be tricky if you're not accustomed to it. This Fast Fact will accustom you, and you'll be addressing the young ladies with ease!

If the daughter is addressed by Miss or Lady, and if she’s addressed by her first name or her family name, such as Miss Julie vs Miss Sweet, depends on the title her father holds, if she’s the eldest daughter or a younger daughter, and if she’s the only daughter present regardless of being younger.

Only daughters of dukes, marquesses, and earls will sport the "Lady" honourific, and their first name will always be paired with that, never ever their family name, and especially never ever the title (which is carried only by the aristocrat’s wife). Lady Julie would be the correct address. This would not matter if she were the eldest or youngest, as they would all be Lady First Name. Lady Julie, Lady Jane, Lady Mary, etc.

The daughters of viscounts, barons, and baronets are addressed the same as the daughters of gentlemen (gentry): Miss Family Name for the eldest and Miss First Name for the younger. Miss Sweet, Miss Julie, Miss Jane, etc.

The rules: if a younger sister is present at an occasion and her eldest sister is not, then she will be addressed as Miss Family Name, but only if an elder sister is not present. The same goes for if the eldest sister marries--the second eldest is now Miss Family Name. So, if Miss Sweet, eldest, and Miss Jane, youngest, attend a soiree, but then Miss Sweet, the eldest, returns home early, leaving Miss Jane at the soiree with her aunt as chaperone, then Miss Jane will be referred to as Miss Sweet.

No one except the closest family members would call someone by their first name only, and even then, it was not uncommon between spouses to maintain the respect, e.g. Mrs. Bennet calling her husband Mr. Bennet rather than calling him by his first name. Even close friends, especially gentlemen, would maintain the respectful address rather than the forename, such as Bingley and Darcy addressing each other as Bingley and Darcy rather than Fitzwilliam, etc.

As an aside, to keep things simple in novels, we tend to stick to one address for ease of identification, so in a novel, don’t be surprised if Miss Jane remains Miss Jane with or without her sister present. This is for the reader’s convenience so the characters are not confused, never mind that it is not the correct form of address. Since the reader cannot so easily see the characters being represented and only knows them by name, consistency helps. If this were happening in person or on the big screen, the correct form of address should be used.

The previous note is not to excuse the use of incorrect forms of address, merely to clarify that if you see Miss Jane not suddenly becoming Miss Sweet when her eldest sister isn’t present, it likely could be intentional on the part of the author, just as writers will often (erroneously) use a titled hero’s first and last name before his title, such as Cecil Sweet, Earl of Macchiato. The correct wording would be Cecil, Earl of Macchiato. To include the family name is incorrect. But in novel writing, writers will intentionally include it so the reader knows the character’s name and can easier identify family members by the family name. Things to take into consideration when reading—writers often make adjustments intentionally for the readers’ benefit. 😉 

For more depth on the subject aside from the graphic provided, I recommend checking out these resources (the Chinet link is a must to bookmark. This is the definitive chart on how to address the peerage!):

Golden Romance Research: Nobility

Golden Romance Research: Courtesy Titles

Chinet's Forms of Address