The words little and Iowa are, in this case, adjectives describing where and how big the TOWN

A town, across the river in West Glen Iowa, has a population of only 500 people.

In this case the subject is town, and the verb is has.

‘Subject’ doesn’t mean what the sentence is talking about. Technically it is “the thing that does the action of the verb” (in the case of an active verb.) The verb ‘to be’ is somewhat difficult to think of in terms of a ‘doing’ word but the town is, nevertheless, ‘being’ “across the river”, so it is ‘the town’ which is the subject. There is no object, as such, in this case. Some people would define ‘subject’ as ‘the little Iowa town of West Glen’ but this is not really correct. ‘Town’ is the true subject and the other things merely serve to qualify or define it.

The sentence is equivalent to “The sun is hot” or “The tower is high”. The part following the verb merely describes or defines the subject, so it is adjectival.

Across the river is the little Iowa town of West Glen, and it’s population is only 500.

subject: West Glen.

verb or verb phrase: none

Verb: is

The way you fixed the run-on is correct.