There are also many demonstrations held in the country and in other countries. Has there been such a vast opposition with a US president inauguration after American Civil War?
A large group of people boycotted Richard Nixon's second inauguration ceremony in 1973. However there are those who say that the numbers were overstated by the media (see citations below).
The honor—or infamy—of being the first to be formally boycotted by legislators goes instead to Richard Nixon’s second inauguration, in 1973. At the time, the Library of Congress told the Washington Post that the action by lawmakers was the first known example of its kind. Stephen Stathis, a Library specialist in inaugurations, noted that individual representatives had stayed away from the ceremony in the past “because of personal hostility,” but that the “large scale” boycott was new to him.
A later rundown by CBS put the boycott figure at 80 members of Congress. The UPI at the time, in advance of the inauguration, quoted Rep. Edwards that the figure would be closer to 165;
In order to compare the numbers, Note that the percentage is actually about the same in both cases
1973 - 255 Democrats, 180 Republicans - 80/255 = 31.4%
2015 - 188 Democrats, 246 Republicans
2017 - 190 Democrats, 240 Republicans, 2 vacancies (1 of each party)
60/190 = 31.5%
More than 50 House Democrats are refusing to watch as Mr Trump is sworn in as the 45th US president.
According to Arizona State University historian Brooks Simpson, 80 lawmakers missed Richard Nixon's 1973 swearing-in ceremony.
Roughly 60 House Democrats, or nearly one-third of the 194-member caucus, plan to be elsewhere when Mr. Trump takes the oath of office, citing objections from Russian hacking to his feud with Rep. John Lewis of Georgia.
Several news outlets, including CBS and MSNBC, have reported that 80 lawmakers wound up skipping the 1973 swearing-in, but Senate historian Betty Koed said that boycott fizzled almost entirely.
“[It] never seemed to happen,” Ms. Koed told the McClatchy News Service. “In the end, there was the usual attendance.”
I don't think a low turnout is of much consequence. You can't expect a massive turnout of people in a region which almost unanimously voted for Hillary (90.5%).
The same was true in 2001 when Bush got elected. He lost very badly in DC with merely 9% of the votes.
As we can see in the Inauguration count for 1993 to 2013, Bush only saw an attendance of 300,000 people in his inauguration. While Obama was well ahead at 1.8 million in 2009. And as expected, his performance in DC was really good with 92.5% of the votes.
It is a complete non issue and should not be given much credence.