Whether or not you're planning to write a series, having a phone directory for your characters and the places they shop can be handy for you. Think-about your town's phone book. It will not only have the name and phone number, but also the address, the town (if it covers more than one metropolitan area), and sometimes the zip code. While I don't advocate using something that could be an actual phone number (in case anyone ever gets hold of your directory), the ever-popular prefix 555 can be a substitute that won't get you in hot water with real people.
You may want to divide your character phone directory into categories, just like the real thing: White Pages for home listings, Yellow Pages for businesses, Government Pages for things like City Hall, the Fire Department, Police or Sheriff's Department, etc. You can get as creative as you wish, but you don't have to get elaborate. This is just a guide for you, the writer. I do suggest putting letters in (A, B, C, etc.) for the surnames, and, just like a real phone book, put Surname first, followed by First & Middle names or initials.
I've started one for my small town where I hope to set a series of books. I have all of the above. My "Yellow Pages" aren't yellow, but I did divide the business listings from the personal listings. I scoured my manuscript, and every time I ran across a new name, I listed it in my directory. (That's one neat thing: you don't have to worry about having unlisted characters!) That way, they're there for future reference. I also added surnames for just about every letter in the alphabet, so I have plenty of room to be creative in adding future characters.
While you're in the process of creating your town or city is a great time to start a directory. However, if you already have several books in your series, it isn't too late. It may be a little more time-consuming, adding in the characters and their addresses and phone numbers, but it will help you in the long run.