I am trying to find the number of individuals in the US that have
accounts at multiple financial institutions.
Also trying to find the same number for small businesses in the US.

Ideally it would be great to know the distribution i.e. how many have
2 accounts, how many has 3 accounts, 4 accounts etc.  But if that is
not possible even the number that have more than one would be fine. 
Note that I mean that these accounts need to be at different
institutions and not two or three accounts with the same bank.

<Multiple bank accounts.

A survey of 4,000 adults holding accounts with financial institutions
in the 20 largest US metroplitan markets found that 75% have
relationships with four or more financial institutions and 65% with
five or more.
Source: A.T. Kearney.
http://www.atkearney.com/main.taf?p=5,3,1,116,4

The average U.S. houshold has relationships with six different
financial institutions.
Source: Kitchenman 2000.
http://216.239.59.104/search?q=cache:f3Z7TT07GK0J:www.privacyalliance.org/resources/glassman.pdf+%22accounts+with%22+%22different+financial%22+survey&hl=nl&ct=clnk&cd=3

The average online consumer currently maintains relationships with
four financial institutions for banking, brokerage, investments, and
insurance.
Source: Forrester.
http://www.internetnews.com/bus-news/article.php/34601

In the U.S. each consumer deals with an average of seven different
financial institutions.
Source: Cash kiosk chamelion. Andy Holloway.
http://www.canadianbusiness.com/article.jsp?content=21339

Typical customers use an average of three financial institutions.
Source: American Society of Business and Behavioural Sciences.
http://www.asbbs.org/files/marketing.pdf


48% of investors have accounts with two or more brokerage firms.
Source: Harris Interactive.
http://www.sia.com/publications/pdf/Investorsurvey2003.pdf

Small and mid-sized businesses typically use multiple financial
providers. More than 40% receive the majority of their loans and
credit card products from sources other than their primary bank.
Source: Small Business Payments in 2006. BAI. 
http://216.239.59.104/search?q=cache:mZJ7Zgkh1pkJ:www.bai.org/pdf/smallbizreport_f.pdf+%22businesses%22+%22multiple+financial%22+respondents&hl=nl&ct=clnk&cd=3

62% reported their business obtained its primary credit card from a
financial institution other than their company?s primary bank.
Source: Edgar Dunn & Company and Collective Dynamics LLC.
http://www.edgardunn.com/newsEvents/pressreleases.cfm?showDetail=100013&xobj=100003

83% of large corporations (businesses with 10,000 employees or more)
have accounts with two or more banks.
Source: Federal Bank of New York. July 2004.
http://www.ny.frb.org/banking/opportunities.pdf>


<Search strategy:>

<"accounts with" "different financial" survey>
<://www.google.com/search?q=%22accounts+with%22+%22different+financial%22+survey&hl=nl&lr=&start=10&sa=N>

<"bank accounts" "or more banks" respondents>
<://www.google.com/search?sourceid=navclient&ie=UTF-8&rls=GGLG,GGLG:2006-26,GGLG:en&q=%22bank+accounts%22+%22or+more+banks%22+respondents>

<"accounts with" "two or more" respondents americans>
<://www.google.com/search?hl=nl&rls=GGLG%2CGGLG%3A2006-26%2CGGLG%3Aen&q=%22accounts+with%22+%22two+or+more%22+respondents+americans&lr=>

<"businesses"  "multiple financial" respondents>
://www.google.com/search?hl=nl&rls=GGLG%2CGGLG%3A2006-26%2CGGLG%3Aen&q=%22businesses%22++%22multiple+financial%22+respondents&lr=

<Hope this helps.>