let response = {
    "locationData": {
        "countryCode": "US",
        "stateName":"Massachusetts",
        "stateCode":"MA",
        "cityName": "Boston, MA",
        // ... (other fields)
    }
};

if (response.locationData.stateCode === "MA") {
    console.log("The user is from the state of ", response.locationData.stateName)
}

response = {
    "locationData": {
        "countryCode": "US",
        "stateName":"Massachusetts",
        "stateCode":"MA",
        "cityName": "Boston, MA",
        # ... (other fields)
    }
}

if response['locationData']['countryCode'] == "US":
    print("The user is from the state of ", response['locationData']['stateName'])

package main

import (
	"fmt"
	"strings"
)

var response = map[string]map[string]string{
	"locationData": {
		"countryCode": "US",
    "stateName": "Massachusetts",
    "stateCode": "MA",
		"cityName": "Boston, MA",
	},
}

func main() {
	if response["locationData"]["stateCode"] == "MA" {
		fmt.Println("The user is from the state of ", strings.Split(response["locationData"]["stateName"], ", ")[1])
	}
}

Determining US territories (Including Puerto Rico, minor outlying islands)

Since the Fastah API response uses standard ISO2 country codes "PR" for Puerto Rico and "GU" for Guam, it's easy to check membership of a predefined set that represents all US jurisdictions of interest.

// List of ISO2 codes for all US jurisdictions
const usJurisdictionsISO2 = ['US', 'PR', 'GU', 'AS', 'MP', 'VI', 'UM', 'FM', 'MH', 'PW'];
// List of US jurisdictions including Diego Garcia aka 'IO' (the British Indian Ocean Territory)
const usJurisdictionsISO2 = ['US', 'PR', 'GU', 'AS', 'MP', 'VI', 'UM', 'FM', 'MH', 'PW', 'IO'];

let response = {
    // ... (other fields)
    locationData: {
        countryCode: 'US',
        // ... (other fields)
    }
};

if (usJurisdictionsISO2.includes(response.locationData.countryCode)) {
    console.log("The user is visiting from a US jurisdiction");
}

package main

import "fmt"

// List of ISO2 codes for all US jurisdictions
var usJurisdictionsISO2 = []string{"US", "PR", "GU", "AS", "MP", "VI", "UM", "FM", "MH", "PW"}
// .. list with Diego Garcia (IO) added
var usJurisdictionsISO2 = []string{"US", "PR", "GU", "AS", "MP", "VI", "UM", "FM", "MH", "PW", "IO"}

var response = map[string]interface{}{
    // ... (other fields)
    "locationData": map[string]interface{}{
        "countryCode": "US",
        // ... (other fields)
    },
}

func main() {
    countryCode := response["locationData"].(map[string]interface{})["countryCode"]
    for _, jurisdiction := range usJurisdictionsISO2 {
        if countryCode == jurisdiction {
            fmt.Println("The user is visiting from a US jurisdiction")
            break
        }
    }
}

# List of ISO2 codes for all US jurisdictions. Add 'IO' for Diego Garcia.
us_jurisdictions_iso2 = ['US', 'PR', 'GU', 'AS', 'MP', 'VI', 'UM', 'FM', 'MH', 'PW']

response = {
    # ... (other fields)
    'locationData': {
        'countryCode': 'US',
        # ... (other fields)
    }
}

if response['locationData']['countryCode'] in us_jurisdictions_iso2:
    print("The user is visiting from a US jurisdiction")