Our D did her college research well and we visited her top three colleges she wished to apply to in October of her high school senior year during her Fall school break, about 2 weeks before her first ED college application deadline. It helped solidify her decision of ED and EA application choices. We highly recommend visiting colleges when classes are in session. One of the three top colleges we visited happened to be on Fall break, too. A college visit leaves a lot to be desired when classes are not in session and most students and faculty aren’t there.
We started tours winter/spring of Junior year. Since my youngest was interested in athletics, he started contacting coaches (with my prodding) around winter break Junior year. Both kids knew they wanted smaller schools - my daughter wanted a city and my son suburban/rural - so I guess the process of elimination began sooner.
I posted earlier that we started with our kids spring of junior year. At this point, my S19 losing steam on visiting schools, but we are not quite done. His number one choice is my alma mater and where his sister attends. But I have encouraged him to look around at other schools. He has visited 5 schools and plans to apply to 4 of them. We will visit 2 or 3 more this summer and in the fall–all within driving distance. The one thing to consider is that some schools do track demonstrated interest. S19 may apply to one school that has a reputation for tracking interest and/or campus visits but we will most likely not get there. The school is coming to son’s HS and he will go to the info session so that will have to do. If he really likes it, maybe we will fly in for a weekend visit.
For S we started in the summer of his sophomore year. Made dedicated trips and fit some to visits to grandparents and even a few business trips. For D22, she has had exposure to a few campuses already but will tour in earnest just like her bro.
S1 - applied to one college with guaranteed admission, sight-unseen. He had been on some other campuses, mostly to baseball fields, but never on a tour.
D - I dragged her along during her junior year to tour S1’s college after he put down his deposit, but the other 7 she applied to she had never seen. She re-toured after acceptance and toured one other where she got good financial aid.
S2 - Had toured our local U with his HS, and Cal Poly where my sister lives. The other four applications were to colleges he had seen on-line only. We did fly out to accepted student days.
A big part of it is knowing your kids. They knew enough about themselves not to apply to Liberty or Oral Roberts but could have done well just about anywhere else. For us, using vacation to tour colleges would have been a huge waste of time.
None of the three likes shopping.
I think there’s no one right answer. It varies enormously with the kid, the budget, the region…
For our part, we did a LOT of visiting because our #1 kid derived very little from catalogs and websites, and the visits taught him (and us) a lot about what he was looking for. And we started relatively early, not because we intended to visit that many schools, but because we didn’t want to squander an opportunity if we were in a given location and not likely to be back later. So there were were probably four visits sophomore year, and then a ton junior year, and a handful senior year. In the end, he went to a school he hadn’t visited until admitted students day, but the prior visits to other schools informed that choice.
I do think it’s very important to do some visits junior year. Currently standing by to see if #2 is interested in doing anything sooner and/or if travel takes us to a place that it makes sense to check out while we have the opportunity.
We started rising junior summer and finished by end of junior spring semester. Long weekends and HS breaks during the junior fall and spring semesters are great since they let you see the actual college kids on campus.
We used the rising senior summer for refining the list, ACT prep, essay writing, resume writing and generally getting organized for the senior fall crazy time rodeo.
We did ZERO tours 
My family is probably an outlier. We did our first tour when my son was in 7th grade and my daughter was in 5th grade. He is now entering high school and has toured four universities (for the record, Duke, UVA, UGA, and Bama). He has also done camps at UVA, UNC-W, and Auburn. Why so early? Fair question. If we are in an area and there is a remote chance our kids might be interested in a university, what’s two hours? We take a look. We fully recognize that their interests and passions may change (they haven’t in ten years, but they might…one wants to work for the Mouse, the other wants to design ships). Second, at home there is no good university campus. The university is a commuter school. So, it is better to give the idea of what college can be like. We’ve made a point to drive though Virginia Tech and Clemson. We want to learn what our kids like, big towns, small towns, college towns, cities? It all helps. Exposure is important. The best advice my, now, high schooler has ever been given is to go to college information sessions, even as a ninth grader. Watch the seniors and juniors. Ask questions. Find out what is out there. Try on different schools. It is a big decision. Get as much information as you can.
Of course, it probably doesn’t hurt that back in the day, I was a tour guide at my alma mater.
Our oldest is a slow decision maker. So in the Spring of sophomore year we looked at a few drivable colleges to figure out city versus suburban versus college town versus rural. That was incredibly helpful for him (and ultimately for his younger brother) and allowed for a much more focused college search junior year.
We are taking D21 on Monday for her first official visit (she’ll start sophomore year in the Fall). It’s Private College Week in our state with special tours and admission programs offered. We are headed 3 hours away to have her look at a very small campus that is the only one in our state offering a specialized guaranteed acceptance doctorate program she is thinking she is interested in. We want to learn more about the program, and what courses she’ll need to take the remainder of HS to be competitive for acceptance into the program. Not a bad idea too to see a very small campus and get a feel for the size. I never toured any campuses. My parents told me where they thought I should apply and I ended up being 3rd generation at their alma mater. I loved it and ended up working 3 years in admissions as a tour guide. Unfortunately, we all agree it wouldn’t be the best fit for D21, so the legacy ends.