You can find this on IPEDS. Among all 4 year not-for-profit colleges in the US, the average over the past decade was a 2% increase in acceptance rate. However, most on this site focus on selective colleges. Most selective colleges have a different trend than the overall average. Among somewhat selective colleges, the acceptance rate has an increasing trend over the past decade at only approximately 1/3 of them. Some of these include:
Denison – Median of past 3 years: 44% acceptance rate, 10 years ago: 39% acceptance rate
Boston College – Median of past 3 years: 31% acceptance rate, 10 years ago: 27% acceptance rate
William and Mary – Median of past 3 years: 36% acceptance rate, 10 years ago: 34% acceptance rate
Note that none of the above are extremely selective. Among extremely selective colleges with a <20% acceptance rate and high test scores, all had a decrease. Some of the ones with the smallest change in acceptance rate are:
Williams – Median of past 3 years: 15% acceptance rate, 10 years ago: 19% acceptance rate
USAFA – Median of past 3 years: 14% acceptance rate, 10 years ago: 18% acceptance rate
WUSTL – Median of past 3 years: 16% acceptance rate, 10 years ago: 21% acceptance rate
At the other end, some of the highly selective colleges with the largest decrease in acceptance rate are::
Chicago – Median of past 3 years: 8% acceptance rate, 10 years ago: 38% acceptance rate
Northwestern – Median of past 3 years: 9% acceptance rate, 10 years ago: 30% acceptance rate
Vanderbilt – Median of past 3 years: 10% acceptance rate, 10 years ago: 33% acceptance rate