Asp.net - Persisting GridView Data Across PostBacks?

Alright, so here's my basic ASP.NET page setup: I've got a page with a GridView that has ContentTemplates in it. You can add a row and edit/remove rows at any time. There's a "New" button that creates a new row.

All of this data is bound to custom data objects. So if I have a GridView of "People" and each row has "FirstName", "LastName", and "Gender" (with TextBox and DropDown controls), I then have a "Person" object which has public properties for "FirstName", "LastName", etc. I have the binding set up correctly, and I can push data into the GridView from the object, and I persist the object with the Session variable. My page lifetime structure looks something like this:

Page_Load: Loads the List(Of Person) from Session()
Any events fire, and modify the List(Of Person).

After any event, the List(Of Person) gets saved back into Session(), and is then DataBound to the GridView (and any subsequent fields are also DataBound, such as the DropDownList.

My question is: Whenever I fill in rows in the GridView, and then add a new row (there is no database saving going on whatsoever), my fields clear out and don't persist across PostBacks. So, how can I persist my custom data objects with databinding across postbacks?