WebAPI - cache States info

I have a C# Core 2.0 Web API controller named 'PersonController' that handles AJAX calls from a front-end.

One of the things that this API does in its POST/PUT calls is check the validity of the person's state code (e.g., "NY") and zipcode which have been passed to the method.

Now, I have a 'lkupStates' table in my database.  It includes such columns as StateCode, StateName, StateCapitol, ZipCodeLow, ZipCodeHigh, etc.  Since this info never changes, it only makes sense to cache this info, although I only need some of it (StateCode, ZipCodeLow, and ZipCodeHigh).

My first question is whether to declare a static variable (e.g., '_dictStateInfo') within the 'PersonController' class, use 'services.AddMemoryCache()', or perhaps implement some other approach?

Whatever is preferable, do I initialize it in the PersonController's constructor or in Startup.cs or some other place?

I've tried using the code below in the PersonController's constructor to retrieve the info from the database:

        public void ProviderController(IMemoryCache memoryCache)
        {
            _cache = memoryCache;

            // STATES
            var stateInfo = _db.lkupStateCode
                            .Select
                             (s => new
                               {
                                s.StateCode,
                                zipInfo = new 
                                {
                                    s.ZipLOW,
                                    s.ZipHIGH
                                }
                               }
                             )
                            .AsNoTracking()
                            .ToDictionary(s => s.StateCode, s => s.zipInfo);
            //_dictStateInfo = stateInfo;
            //_cache.Set("dictStateInfo", stateInfo);
        }

For some reason, the constructor never gets called.  So I moved the database call to another section of the code, and the call worked just fine.

I then tried to go the static variable route by first defining a class:

public class ZipInfo
    {
        public decimal ZipLOW { get; set; }
        public decimal ZipHIGH { get; set; }
    }

Then declaring a private, static class-level property:

private static Dictionary<string, ZipInfo> _dictStateInfo;

And then assigning the results of the EF call:

_dictStateInfo = stateInfo ;

But it got flagged as an error -- Visual Studio effectively said that it couldn't convert from the LINQ's anonymous "zipInfo" to the _dictStateInfo's "ZipInfo" class.  I suppose I could smooth things out by using the 'lkupStates' class model, but that seems like a waste of memory, since I don't need all the fields.

I would have tried going the cache route by initializing the cache also in the PersonController's constructor:

_cache.Set("dictStateInfo", stateInfo);

But since the constructor never got called, when I tried to pull it out:

 if (false == _cache.TryGetValue("dictStateInfo", out Dictionary<string, ZipInfo> cacheStateInfo))

I get a "System.NullReferenceException", and indeed _cache == null

Your help would be greatly appreciated -- and despite all the foregoing, my end goal is very simple: cache (hopefully selected) data from my 'lkupStates' table.

P.S. - and yes, I understand that one big hole in the above is the constructor not being called, but I theoretically can work around that by using a static variable and migrating the code elsewhere ... that said, help getting the constructor to execute would also be greatly appreciated!