That can be the source for this information. If not, common sense can often help you identify your markets and your customers. We're not talking about a complex study here. Just take a look at your customer base. Be sure you understand clearly your mission and its scope, for it justifies your library's existence and defines the parameters of your marketing decisions.
Marketing encourages a focused approach to meeting customer demands.
The non-marketing, shotgun approach has been the downfall of more than one library. Make sure you target specific library products and services to defined, manageable groups of customers. Maybe it's time to be selective about who you serve and what you provide. Take your cue from the decline in department stores. They try to offer everything, but now their customers are gravitating towards smaller specialty shops with targeted products.