Can parents force an 18 year old to go to college in Mississippi?

yes

So which is it 18 or 20 living with a gf? Better hide your history dude.

No even in Mississppi your @ss is an adult at 18 and but if you don't then you should be prepared to move out. They don't have to keep letting you live under their roof if you aren't prepared to live by their rules. They can get an eviction notice and kick you out and if you don't go then yeah the cops will come and boot your butt out. Get a job and find a place to live if you think you're too good to get a better education and have make a better life for yourself.

Mississippi's age of majority is older than most states, at 21 years old. However, minors do have some legal rights and responsibilities. For example, under Mississippi law, 18-year olds can enter into contracts and settle personal injury lawsuits.