How many employees do the biggest companies in the US (by number of employees) have?
So, I reviewed the previous answer and then did an independent search to answer your question, and here is what I found.
First off, I found that there is 2012 data available on the largest employers (by employee) from several sources. I chose to use Fortune magazine - a well-respected and long-standing businesses publication - that has been compiling lists of US companies/corporations for years. Fortune compiles the list as follows below. (Note: I have also included, in parentheses, their rank by total revenues in 2012, which is the metric that Fortune typically uses.)
Walmart - 2,200,000 employees (#1 in revenues)
McDonalds - 420,000 (#110)
IBM - 412,775 (#24)
Kroger - 400,000 (#20)
Home Depot - 371,000 (#33)
Target - 347,000 (#36)
UPS - 336,150 (#47)
Berkshire Hathaway - 316,000 (#4)
General Electric - 305,000 (#8)
Yum Brands - 303,405 (#228)
I double checked this in a couple places, and the only deviation was that I saw was that a 2013 online publication substitutes Berkshire Hathaway in the list above for Hewlett Packard. *But*, HP laid off nearly 30,000 people from 2012 - 2014, so it is entirely possible that that source did not account for these rolling layoffs, which we strategically staged and reported by HP. My money is that Fortune - who is in the know as much as any industry source - got their numbers right.
The late 1970s, and 1977 in particular, is largely recognized as the beginning of a massive change in the US economy from manufacturing to service-oriented, as well as numerous other changes on the global stage, caused by a number of factors.
Unfortunately, after a long and extensive search of online, website, magazine, and even academic sources, I cannot find a listing of largest firms *by employee* for 1977, or any year in the 1970s or early 1980s for that matter. It is just not available in any consolidated list, or piecemeal, that I could find anywhere, and as a professional urban planner who works with data like this all the time, I looked in numerous places and still was unable to locate it. I could do what the previous researched did and try to find the employee counts of the CURRENT top 10, but that is not helpful for your purposes as you already noted.
So, here are the largest employers by revenue in 1977:
Exxon Mobil - 48.6 billion
General Motors - 47.2 billion
Ford Motor - 28.8 billion
Texaco - 26.5 billion
Mobil - 26.1 billion
ChevronTexaco - 19.4 billion
Gulf Oil - 16.5 billion
IBM - 16.3 billion
General Electric - 15.7 billion
Chrysler - 15.5 billion
Oil companies dominated the list, and were making huge revenues even then!
What I was able to find was the top employment by industry sectors in 1977 vs. 2015, listed below:
Mining - 854,00 employees (1977) vs 843,000 employees (2015)
Construction - 3.9 million vs. 6.4 million
Manufacturing - 19.6 million vs. 12.3 million
Transportation/Public Utilities - 4.6 million vs. 26.9 million
Retail Finance/Insurance - 18.4 vs. 15.6 million
Services - 15.5 million vs. 62.4 million
Government - 15.4 million vs. 21.9 million
It would not be helpful to try and make employment projections on the data we do have because, as mentioned and as I am sure you know, the US economy has changed so much that a simple or even complex projection would not be accurate doe to globalization, market sector shift, population growth, and regulatory changes, among numerous other factors.
For reference and interest, here is the accounting of the top 10 US companies - by employee - 1955, which I was able to find cited identically in 2 different sources:
General Motors - 576,667 employees
US Steel - 268,142
General Electric - 210,151
Chrysler - 167,18813
Standard Oil of New Jersey - 155,000
Amoco - 135,784
CBS - 117,143
AT&T - 98,141
Goodyear Tire & Rubber - 95,727
Firestone Tire & Rubber - 90,000
I honestly think that to get the data you want, you'll need to get access to proprietary data from a subscription service that generates reports for profit (hence not being available publicly.) If you call a local university or library branch is a large public library, they should be able to provide a reference for a company, and if you join their library (or perhaps ask very nicely) they just might look it up for you. Or, if you have a contact that works in government or for a non-profit, they might have access to such subscription data, too.
Thanks for a very interesting question and for Wondering!