The Marketing/Research Department
At some newspapers, the marketing/research department is a big department, but at others it's a one man show or even a job responsibility of your ad director or general manager.

The marketing/research department works with the circulation and advertising departments to help them market their products better. At most papers, this is the department who was in charge of the market and readership surveys (more on these later) that was used to develop the promotional pieces you'll be using to explain to your customers why you reach enough of the right people in the right places.

This department or person will be invaluable when a potential advertiser tells you they're looking to reach a specific demographic, such as working women over the age of 40 who own their own home. Chances are, the marketing person can look at a demographic survey and tell you exactly how many people your newspaper reaches that fit that target market. There are also some incredible research tools that your newspaper might also have that goes far beyond standard demographic information. I'd suggest finding and introducing yourself to the marketing department/person and see for yourself what resources you have available.