Morris.js for WordPress?

Create js folder in your theme directory then save Morris.js into it. it is not mandatory to store it in js folder you can store it anywhere else but i recommend to do it to seprate javascipt files from other files.

Add follwing action into functions.php file

function custom_scripts() {
/* Include Scripts */
wp_enqueue_script( 'morris-script', get_template_directory_uri() . '/js/Morris.js', array( 'jquery' ), '', true );
}
add_action( 'wp_enqueue_scripts', 'custom_scripts' );

You can find more information about wp_enqueue_script() function from this link http://codex.wordpress.org/Function_Reference/wp_enqueue_script of wordpress codex.