Uncaught TypeError: undefined is not a function on getAttribute method

I have a function where I need to get the 'id' of an element in an array (county).

function returnCountyId(){
   var countyName = findCountyMatchFromServer();
   var foundCounty = county.findBy('title', countyName);
   var countyId = foundCounty.getAttribute('id');
   return countyId
}

I find the name (countyName) but somehow

foundCounty.getAttribute('id');

returns error: Uncaught TypeError: undefined is not a function

Rest of the code:

function findCountyMatchFromServer(){
   var county = getElementAsString("ddlCounty");
   return county;
};  

var county = [{
   id: '1',
   title: "Harjumaa",
   avgPrice: '1234',
   avgSurface: '23',
}, {
   id: '2',
   title: 'Hiiumaa',
   avgPrice: '5345',
   avgSurface: '243',
}]

Thank you!