Retrieve Taxonomy Term ID from Term Name?

I am using the following code to do a query on my database from within my page template by using the term_taxonomy_id which I retrieve from the end of the URL.

My URL looks something like this when using this template http://mysite.com/county/18 with 18 in this case being the term_taxonomy_id

My code is as follows:

 <?php
 /*
 Template Name: County
 */
 $ex = explode("/",$_SERVER['REQUEST_URI']);
 //print_r($ex);

get_header(); 

// Global query variable
 global $woo_options; 
 global $wp_query;
 global $wpdb;
 $all_terms = $wpdb->get_results("SELECT *  FROM wp_term_taxonomy,wp_terms WHERE wp_term_taxonomy.parent='{$ex[2]}' AND wp_term_taxonomy.term_id=wp_terms.term_id ORDER BY wp_terms.name");

 //echo "SELECT name   FROM wp_terms WHERE term_id='{$ex[2]}'";
 $taxName = $wpdb->get_results("SELECT name   FROM wp_terms WHERE term_id='{$ex[2]}'");
 foreach ( $taxName as $tx ) {

 $nameTaxnaomy = $tx->name;
 }

 $getPostID = $wpdb->get_results("SELECT object_id   FROM wp_term_relationships WHERE term_taxonomy_id='{$ex[2]}'");
 foreach ( $getPostID as $tx1 ) {

  $post = $tx1->object_id;
 }

 ?>

Question:
I however need to change my URL structure to use the term_name at the end of the URL and not the taxonomy_id as above.

So now my URL looks like this http://mysite.com/county/London

When I do this, the database query does not work as it is exploding the URL to get the taxonomy_id at the end (18 in my example above) and then query the DB using that string.

Actual Question: Is there a way to get the term_taxonomy_id from the term name so I can use it in my db query?

I am thinking something like

//explode the url to get the term name
$dx = explode("/",$_SERVER['REQUEST_URI']);

//now get the id from the term name
$ex = //get the term_taxonomy_id from $dx 

Any help appreciated

Cheers

Update – With some tips below I have made the string look like this. My taxonomy name is called location

//define $ex byt ge_term_by
$ex = get_term_by('slug',explode("/",$_SERVER['REQUEST_URI']),'location');

When I echo $ex I don’t get anything so something wrong still 🙁