I have been recently hired by a US based company to code on their platform. Living in a different country, how can I verify that the company is legit and how do I find any information regarding the company. Like in my country the government has a portal where I can check the registration details of the company including the registered office address, board members, paid up capital etc. I have requested the registration information of the company and they have provided me with the registration file number. But I cant find an official site, where I can cross verify them. Any help would be appreciated.
As was mentioned in a comment, in the United States, businesses are generally registered at the state level. The information collected, and the extent to which or manner in which the public has access to it, varies from state to state. There may still be states where that's a paper-only process, but I'd guess in most of them it's accessible online, at least for basic information. For example, in Michigan the Department of Licensing and Regulatory Affairs has a Business Entity Search tool.
If a business deals directly with consumers, it may be a member of the Better Business Bureau. Even if it isn't, but consumers have complained about it, the BBB will make public the information it has about the purported business.
If a company is publicly traded (that is, it's corporation that issues stock, and the stock is traded on a stock exchange), it is required by law to be registered with the Securities and Exchange Commission. The SEC's EDGAR tool will display the company's filings, which should include annual and quarterly reports.
If the company is or wants to be a government contractor, it generally needs to register with the General Services Administration, and certain information about successfully registered entities is publicly viewable in that system. (Conversely, the same system also lists "Excluded Parties" who are prohibited or partially restricted from doing business with the government.)
Depending on what the business does, it may also be subject to registration with and regulation by additional state or federal agencies.
For a full picture, however, unless you're dealing with the obvious agent of a Fortune 500 company, you'll probably want to get information from a private credit-check service as well; for example, as also mentioned in a comment, Dun & Bradstreet for the business itself, or for a really small business a personal credit report on each of the owners and officers.