Where can I acquire the blueprints for my home?

Perhaps the firm that built it ?

It’s not a new home. It’s about 50–60 years old. How would I go about discovering which firm built it?

I’ve tried measuring it myself, but there are inches missing and I’ve given up.

I am not sure, but here i think such info is kept at city hall or some such….

Contact your county recorder’s office.

@hungryhungryhortence You beat me to it. The county recorder’s office.

Thanks, is the county recorder likely to be in city hall? Do they have any other types of names?

No, the county recorder is more likely to be in the county office building. Usually the city and county are two different things. Some cities and counties have the same name, such as Sacramento, and Denver, but they are two different offices.

You could also try the city or county planning agencies.