You can pull the data from {site url}/about.json, and get the users_count key’s value. For example on Meta:
{
"about": {
"stats": {
"topics_last_day": 16,
"topics_7_days": 99,
"topics_30_days": 553,
"topics_count": 60801,
"posts_last_day": 549,
"posts_7_days": 3352,
"posts_30_days": 19273,
"posts_count": 1722045,
"users_last_day": 23,
"users_7_days": 132,
"users_30_days": 713,
"users_count": 61086, // This value here!
"active_users_last_day": 535,
"active_users_7_days": 1219,
"active_users_30_days": 2518,
"likes_last_day": 169,
"likes_7_days": 1547,
"likes_30_days": 10833,
"likes_count": 1641538,
"participating_users_last_day": 119,
"participating_users_7_days": 373,
"participating_users_30_days": 912,
"visitors_last_day": 2161,
"visitors_7_days": 4468,
"visitors_30_days": 8669,
"eu_visitors_last_day": 653,
"eu_visitors_7_days": 1206,
"eu_visitors_30_days": 2022,
"chat_messages_last_day": 72,
"chat_messages_7_days": 707,
"chat_messages_30_days": 3015,
"chat_messages_previous_30_days": 3621,
"chat_messages_count": 99670,
"chat_users_last_day": 8,
"chat_users_7_days": 27,
"chat_users_30_days": 67,
"chat_users_previous_30_days": 87,
"chat_users_count": 925,
"chat_channels_last_day": 3,
"chat_channels_7_days": 8,
"chat_channels_30_days": 39,
"chat_channels_previous_30_days": 36,
"chat_channels_count": 3117
},
"description": "Learn about and discuss Discourse, the next-generation open-source forum software.",
"extended_site_description": "<p>A place for the Discourse community to meet, ask questions, provide support to one other, and share much-appreciated feedback.</p>",
"banner_image": "https://d11a6trkgmumsb.cloudfront.net/original/4X/8/3/5/835377a3ea23f75e6c6c08ed3d7d606a0f2c3e72.jpeg",
"site_creation_date": "2016-02-17T07:50:40.228Z",
"title": "Discourse Meta",
"locale": "en",
"version": "3.6.0.beta1-dev",
"https": true,
"can_see_about_stats": true,
"contact_url": "",
"contact_email": "team@discourse.org",
"moderator_ids": [
127856,
112395,
8307,
8571,
140271
],
"admin_ids": [],
"category_moderators": []
}
}
the users_count number is 61086.