Postal votes also now. Ad astra per aspera
One of the reason why contested county elections were so expensive was the need for candidates to bring the electors to the polling place. For example in Middlesex, the second smallest of the counties of England, most of the voters lived in the east of the county in and around the City of London. However the county poll was held at Brentford, in the west of the county. I have seen advertisements in early nineteenth century editions of The Times where candidates advertised times for their supporters to catch a coach from London that the candidate provided. No doubt the problems were even worse in the larger counties.
As the electorate increased and poorer people began to vote who could not afford to take a day or two off work to go and vote, it was obviously sensible to provide multiple polling places closer to where people actually lived. Thus we end up with at least one polling place in each local government ward.
The wards in Slough, where I live, are quite small geographically; but most wards have several polling districts usually voting in a school or (as for my polling district) in a mobile polling station the Council parks on a convenient patch of grass.