I keep getting prompted about Dearborn, MI

I'm having exactly the same issue. I'm in KC and I have Google Fiber. MacOS seems confused about my location and I am often alerted that a device is trying to login to my iCloud account near Dearborn. Also, websites that use my location data think I'm in Dearborn MI. Google maps always get my location right. Strangely, the Apple Maps app on desktop gets my location right too. But when I logged in to Apple Support Communities just now to write this reply, for instance, it alerted me about a login near Dearborn. The first time I noticed this was when I connected an Amazon Echo Dot and it had my location wrong. I have no idea what's going on...

Does your Mac's Map App show your correct location?

Have you tried to remove any adware which might have managed to get install on Mac?

I'm seeing the exact same thing from KC

Same Issue here, from Austin TX.

I figured on a network path proxy test, Apple.com initiate from Dearborn, MI. You can test at http://www.yougetsignal.com/tools/visual-tracert/

Mine has a similar proxy trace, but what does that mean?

Do you have Google Fiber? I have noticed some similar issues not only with iCloud but with my Amazon Echo so thinking it may be my internet connection.

Same issue here in KC area with Google Fiber. I'd go to a place like bestbuy.com and it always showed me stored in Dearborn.