Drupal 7 - Theme Settings Fieldset (group) of Fields

theme-settings.php

function THEMENAME_form_system_theme_settings_alter(&$form, $form_state, $form_id = NULL){
  // Set up the a fieldset (group) for general information
  $form['general_info'] = array(
    '#type'         => 'fieldset',
    '#title'        => t('General Information'),
    '#description'  => t('General contact information for Duke Health & Fitness Center.'),
  );
  $form['general_info']['address'] = array(
    '#type' => 'textfield',
    '#title' => t('Address'),
    '#default_value' => 'Raleigh, NC 27705',
  );
  $form['general_info']['phone_number'] = array(
    '#type' => 'textfield',
    '#title' => t('Phone Number'),
    '#default_value' => '919-999-9191',
  );
}