Inserting Fields from A Custom Content Type into Custom Form I created a custom content type called 'Building Location' that contains a custom field called 'US_States'.

Is there a way I can access and include the 'US_States' field into a custom form I'm building without having to re-create it with the Form API?

I'm looking to include the same drop down list, 'US_States,' from the 'Building Location' content type in a custom form that is part of a module I'm building, ensuring the two will always have the same options available.
There isn't an API for attaching a single field from an entity to a form, there is one to attach all fields. field_attach_form. I wouldn't suggest you doing that do, since it can quickly become unmaintainable.

Instead I would suggest that you simply get the field options, or allowed values as they are called. That is pretty simple as well.

$info = field_info_field('field_machine_name');
$options = $info['settings']['allowed_values'];