To make comparisons that have analytical meaning, we often need to find comparable proportions. For example, it doesn’t make sense to argue that California is more car-focused than Rhode Island because there are more cars in California. There are also more people in California, so of course the absolute number of cars is going to go up.
However, if we could should that there are more cars per person in California than there are in other states, that might help us argue that California is more car dependent.
If you’r working with county level data, population data broken down by race or gender, or data over multiple years (ie, the population of NY is different in 1790 than it is in 1890), this will be a little more complicated, but the principle is the same.
I’ve made files of US population totals by state and county from 1790-2010 available for you on the Datasets page. If you need totals broken down by race, gender, or other factors, you can create a free account and download your own data from NHGIS.