 <p>I found a solution that works, though I admit I am not sure exactly how it works. I added the line <code>context.Configuration.ProxyCreationEnabled = false;</code> to my method that returns the object collection and all my objects were returned. I got the code from the following <a href="http://stackoverflow.com/questions/8173524/webapi-with-ef-code-first-generates-error-when-having-parent-child-relation">SO Question - WebApi with EF Code First generates error when having parent child relation</a>.</p> <pre><code>public class ClientsController : ApiController { public IEnumerable&lt;Client&gt; GetAllClients() { using (var context = new MyClientModel.MyEntities()) { context.Configuration.ProxyCreationEnabled = false; // ** New code here ** var query = context.Clients.Where(c =&gt; c.State == "CA"); var customers = query.ToList(); return customers; } } } </code></pre>