It had to be when I was traveling for work as part of a transition team. I would spend months at a time in a city, coming home only every other weekend. I can’t say for sure which, but it would say it was probably either the Hyatt Regency in San Francisco or the Adam’s Mark in St. Louis. Or our timeshare, where I’ve spent ~30 weeks.
IOW, damned if I know.
Basic and Advanced Electronics training when I was in the Navy lasted from October '73 thru June '74. I lived in the barracks at NAS Memphis during that time. I never considered it to be home - it was just another stop along the way. I’ve been stationed in quite a few training command, but that stint was the longest.
You fancy. 
I spent years traveling in China in the 1980’s. I guess the longest was about 2 years before renting a really cheap apartment in Hong Kong to call a base. Even then, I would go 2-3 months without returning to that apartment base.
We rented a cabin on Schroon Lake, NY, for over twenty years. Never stayed longer than a week at a time, but it adds up. My wife had been going there for over 50 years when we finally decided not to renew.
I went to the same sleep away camp for a week or two every summer for 7 years. The 8th year I worked there all summer. I would say over the years I spent 20+ weeks there.
The next would be the three months straight I spend living in a hotel on the Peninsula in the Bay Area while working for E*Trade when it was still an internet startup.
If dorm rooms don’t count (and they probably shouldn’t. You live there.), then I think it’s six weeks at summer camp. 5 as a camper, 1 as a counselor.
Twenty something years ago I had to go to a two week software training class in Birmingham AL, and spent two full weeks in a hotel there. Probably the longest two weeks of my life…
Three months in a mobile home in Florida while I was working at a trailer park in the summer.
Two nights every eight days for 15 years in the same fire station. Seven of those years in the same bed. Four years or so total, plus or minus.
Now my office is upstairs in the same fire station, and I only work days. Been that way for a year and a half. Wish I was back downstairs.
I was working for a company with a branch in Nuremberg, Germany. They were trying to get the groups to know one another and work together, so they sent me there for three months. I was in a hotel a few blocks from the office, just outside the old, walled part of the city. They had a few rooms that were for extended stays like this; had a little more space than a regular hotel room, two-burner stove, and a small fridge. I think I was there for just under 90 days, so I didn’t have to get a special work visa. And it happened at a time when my apartment lease was up, so I put my stuff in storage and didn’t have to pay rent for those months.
Other than that was my sailing trip on the Picton Castle. I had a couple weeks in Lunenburg, Nova Scotia, getting the ship ready. Then about three weeks at sea, and another week in the Caribbean. I had the same accommodations the whole time, so I think it counts; main salon, port side, forward, upper bunk.
Not counting dorms, the Inn at Queen Anne in Seattle. Perfect location right next to Seattle Center, so every time I stay overnight in Seattle (about 60 times overall) I stay there.
I spent two plus months in training back in America when I joined a US company in 1999. I stayed a Marriott residence. I did go back to Japan for a week in the middle and had a business trip to New York. The company nicely didn’t make me pack up all of my things so they were paying for two rooms for each night, one of each of the coasts.
I lived in a tipi for four months in the middle of a field in California while a summer farm apprentice. I was 20. Then was I was about 55 I lived in a tent in a sheep pasture in Saskatchewan for a couple summer months while working on a sheep ranch.
I had a job with a military contractor, with an extensive travel requirement.
Longest in any one place was 11+ uninterrupted months (not quite 12) at a Residence Inn in Colorado Springs.
The particular one I stayed at is apparently gone now; it was on Academy & Austin Bluffs.
I did over twenty years working fly in/fly out at a remote minesite
Sleep-away camp when I was a kid. Six weeks each summer, for six summers, so 36 weeks total. Sports writer Thomas Boswell was one of my camp counselors.
As an adult, my wife and son and I have spent a week at the same beach cottage on Anna Maria Island each year for the past 9 years, so that’s 9 weeks and counting.
Ah, yes, a business traveller must always state this for tax purposes!
We were on location in Sicily for three months, but for around two I stayed in a hotel in Palermo. Nothing to do so I just swam in the pool for hours every day, and worked on my tan. A hard job but someone had to do it. 
I’ve also stayed in a summer camp for a month, for two consecutive summers, although we senior teachers stayed in a couple of houses off campus. As there’s no booze allowed on campus I think this is a sensible option.
Not quite as long, but I was in hospital for around six weeks although this was divided between three wards.
Naw, fancy was when I went here - a private boarding school in the same town where the Queen’s drinking water comes from. The guy I shared a bedstudy (like a small dorm room with desks) was the son of the world’s most famous polo breeder. The guy in the next bedstudy was the son of the chairman of a Fortune 100 company. I played rugby against Prince William when he was at Eton.
I went from there to a shitty public school in Florida. You can imagine the culture shock. :eek: